Bike is a slang
term for bicycle
, the two-wheeled human powered vehicle
of childhood and beyond. Bikes are universally loved and enjoyed by the young of both sexes. It, or one of its variants, represent the first vehicle that a young person is allowed to operate. The bike represents freedom, expanded horizons, and the joy of experiencing the wind blowing through the rider's hair as it transports him or her into the future.
Modern bikes usually possess wheels of the same size. They come in different sizes, scaled to the size and ability of the rider.
Bikes may come with various accessories. In the past such items as handle tassles were popular. Horns were also an extra coveted by many. Seats of various types abound, from the common saddle seat to the banana seat and others designed to make the trip more comfortable. Gears are available on all but the more basic models, allowing for easier negotiation of those pesky upgrades.
Bikes of the past often had a huge front wheel and a much smaller rear wheel. Bikes have been made for multiple riders as well as for the solitary bicyclist. Though they have been around for well over 2 centuries, bikes are still the focus of innovation. Better materials, as well as much better engineering, make the vehicle much more dependable than it once was. They are stronger while being lighter, roll much easier and require much less effort to operate than their elderly brethren from days gone by.
In countries other than the US, bikes are far from being an amusement or toy. They are the main means of transportation for a fair percentage of the world's population. They can be used as taxis, for the transport of small goods and delivery vehicles.
As with most things, the term bike can apply to another genre of vehicle. The motorcycle is a variation on the bike. Yes, motorcycles have 2 (or more) wheels. They also are motorized, which makes them a different breed of cat indeed. Motorbikes come from small little 2 stroke putt putts to hugely expensive and luxurious watercooled behemoths. Still, partisans of these motor driven beasts call them bikes. These machines have given rise to their own subculture. Riders have their own style of dress, their own language, establishments which cater to this clientele.
As long as people wish to be mobile, the bike in all its manifestations will be a viable option.