Why do we have to constantly defend this question. I know the OP is asking genuinely but boy oh boy. Maybe we need a solid STICKY defining these. Here is the info from Wikipedia

Hybrid Bike:
A hybrid bicycle is a bicycle designed for general-purpose utility or commuter cycling on paved and unpaved roads, paths, and trails. Also known under such names as City bike, Cross bike, or Commuter,[1] the hybrid takes design features from both the road bike and mountain bike, with the goal of making a bike for general commuting and transportation.
In general, hybrids use the mountain bike's triple crank, together with the latter's handlebars giving a more upright posture than road bicycles. They also usually use one of the kinds of brakes used on mountain bikes, namely linear pull, or disc. From the road bicycle they take the 700C (larger) wheel diameter for higher speeds, but use a wider rim and tire for increased strength. (wikipedia)


Commuter Bike:

The commuter bike is a hybrid designed specifically for commuting over short or long distances. It typically features derailleur gearing, 700C wheels with fairly light 1.125-inch (28 mm) tires, a carrier rack, full fenders, and a frame with suitable mounting points for attachment of various load-carrying baskets or panniers. It sometimes, though not always has an enclosed chainguard to allow a rider to pedal the bike in long pants without entangling them in the chain. A well-equipped commuter bike typically features front and rear lights for use in the early morning or late evening hours encountered at the start or end of a business day.[1]


City Bike
Similar to the commuter bike, the city bike is optimized for the rough-and-tumble of urban commuting.[1] The city bike differs from the familiar European city bike in its mountain bike heritage, gearing, and strong yet lightweight frame construction.[1][3][4][5] It usually features mountain bike-sized (26-inch) wheels, a more upright seating position, and fairly wide 1.5 - 1.95-inch (38 - 50 mm) heavy belted tires designed to shrug off road hazards commonly found in the city, such as broken glass.[1][6] Using a sturdy welded chromoly or aluminum frame derived from the mountain bike, the city bike is more capable at handling urban hazards such as deep potholes, drainage grates, and jumps off city curbs.[1][6] City bikes are designed to have reasonably quick, yet solid and predictable handling, and are normally fitted with full fenders for use in all weather conditions.[1] A few city bikes may have enclosed chainguards, while others may be equipped with suspension forks, similar to mountain bikes. City bikes may also come with front and rear lighting systems for use at night or in bad weather.[1]


Comfort Bike
Another subclass of the hybrid category is the comfort bike. Comfort bikes are essentially modern versions of the old roadster and sports roadster bicycle,[1] though modern comfort bikes are often equipped with derailleur rather than hub gearing. They typically have a modified mountain bike frame with a tall head tube to provide an upright riding position, 26-inch wheels, and 1.75 or 1.95-inch (45 - 50 mm) smooth or semi-slick tires. Comfort bikes typically incorporate such features as front suspension forks, seat post suspension with wide plush saddles, and drop-center, angled North Road style handlebars designed for easy reach while riding in an upright position. Some comfort bikes have hub gears instead of derailleur gears.