There are so many different types of bikes and uses for bicycles that it can be a little difficult to sort it all out or, if you are fairly new to cycling, find the right bike, or bikes that fit your riding style and meet your own personal biking needs.
If you are fairly new to biking, getting more serious, or possibly just getting back into cycling after not riding for some period of time then it is very important to consider your personal riding style and preferences before deciding on a bike type, excluding the other bike categories and researching one particular bike type or bike category in detail.
I've seen quite a few references to common bike types on the internet on informational sites, bike manufacturer sites and on merchant sites (where you actually buy the bikes online). You will find that the names for the bike categories or bicycle types will differ somewhat on each web site.
The listing below is intended to summarize the most common or most popular bicycle types using the most commonly used names (in the US) for the various bicycle types or categories.
Mountain Bikes are designed of "off road" riding and are great for use on back country trails, hills and ravines. Mountain bikes are also popular as all purpose bikes for use on roads, paved and crushed stone trails as well as rugged trails due to their durability.
One of the more important considerations when choosing a mountain bike is the type of suspension that is best for your needs. There are rigid mountain bikes which have no suspension, hard tail mountain bikes which have front suspension but no rear suspension and full suspension models.
Road Bikes are designed for use on roads, tracks and well maintained bike trails. For many years this category was referred to as 10 speed bikes. Today most of these bikes have 3 sprockets in front and multiple sprockets in back so they normally have more than 10 speeds. There are also a number of different types (or sub categories) of road bikes such as Racing Bikes, Touring Bikes and Sport Bikes.
Hybrid Bicycles are a cross between different bicycle types. The most common reference is usually the cross between a mountain bike and a road bike. These bikes usually have tires that are thinner than a mountain bike but wider than a typical road bike (700x35c is common), the handle bars are more like a mountain bike and you sit up straighter than on a road bike. Some hybrid bikes are designed for comfort and all purpose use and many come with shock absorbers (front and/or under the seat) and comfortable seats.
Recumbent Bicycles (also referred to as bents) take advantage of reduced wind resistance, and are fast and comfortable. Recumbent riders sit in a reclined position as opposed to the upright or forward leaning positions of more traditional bikes. Bents are becoming much more popular than in the past and are suited well for touring, bike trails (not rugged mountain trails) and roads.
There are many different configurations of recumbent bikes. There are Short Wheel Base (SWB) where the pedals are above the front wheel, Long Wheel Base (LWB) where the pedals are behind the front wheel, Above Seat Steering (ASS) where the handlebars are usually about chest high, and Under Seat Steering (USS) where the steering is under the riders seat (less common). There are also tandem recumbents in addition to recumbent trikes with the double wheels in front or in back.
BMX & Freestyle Bikes BMX bikes are designed for off road racing on dirt tracks, Freestyle and Jump Bikes (in the same general category) are designed for performing stunts and tricks and jumping ramps. These are usually (but not always) 20 inch bikes with upright handlebars, knobby tires, rear hand brakes and, in some cases, additional front brakes and pegs for stunts.
Cruiser Bicycles (or beach cruisers) are the old style or classic bikes with balloon tires and upright seating position that were popular in the US until around the late 50s. These bikes are comfortable, sturdy, durable and can handle a variety of different terrains. Most cruisers are heavy and usually have just one speed (the downside to their durability).
Kids Bikes are another category altogether. Kids bikes really come in a variety of different styles and sizes. Bikes for kids usually include the 10 inch to 16 inch size bicycles (with or without training wheels) but older kids may also prefer any of the other bike categories above (mountain bikes, bmx, road bikes, etc.).
This category may also include tricycles, scooters, ride-on toys, push toys and other adult bicycle accessories for children such as child seats, bike trailers and kid carriages, and trailer bikes.
OK, now that we've covered the most common and most popular bicycle categories, let's see what else is out there. There is no way that I can cover all of the bike and bike-like types of machines that have been created, invented or are available to purchase, but the list below does cover some of the additional bike or bike-like categories that are fairly popular.
Chopper Bicycles or Low-Rider Bikes - These are usually flashy custom build bikes with extended forks and lots of chrome and/or custom paint jobs that are designed be comfortable and to attract attention.
Folding Bikes - These bikes are designed to fold into a light and compact package for commuting and longer trips where storage is a factor.
Commuter Bikes can be any bicycle type depending on how you are commuting. If you are commuting to work by roads, a road bike might be the best choice, if you are commuting by side roads and bike trails a hybrid or mountain bike may be your choice. What I have found here in the suburbs is that if you are commuting to the train station, leaving your bike at the station, and then taking the train to work, most people choose a "beater" (a stripped down bike with little value) to leave locked at the train station.
Electric Bikes come in a variety of styles but most resemble mountain, hybrid or cruiser bikes. These bikes are human powered (you pedal them like a regular bike) but have a supplemental battery powered motor for help on hills or when you need a break. The batteries are rechargeable and have a limited range (usually around 35 miles).
Utility Bikes can be any bicycle type that is practical for short commutes and everyday errands as opposed to use for recreation or fitness. Utility bikes often include luggage carriers, baskets and/or bike bags.
Although some stores may refer to "comfort bikes" as a bike type or bike category, it is really more of a way to describe any bike style that is comfortable (to you specifically). I believe that the most common types of bikes that most people consider "comfortable" are hybrid bikes, cruiser bikes and recumbent bikes.
You generally sit in a fairly upright position on a hybrid or cruiser bike and these categories often include comfortable seats (saddles) and shock absorbers. Recumbent bikes are a little "out of the norm" but are what would get my vote for the most comfortable of all bikes.
Personally, I consider how much energy it takes to ride a particular bike as part of it's comfort factor. For example, a heavy cruiser bike may have a comfortable seating position but you may feel like you've ridden 10 miles (on a lighter bike) when you have only ridden 1 mile on your cruiser. For short trips this is not that important but if you are going to ride a long distance, this an important consideration.
If you consider the amount of energy it takes as part of the comfort factor, I would also consider electric bikes in this category.