There are bicycles for a wide range of activities, but most people should be considering a bike from one of four main categories

 ROAD BIKES
These are the quickest, either all out racers or fast tourers.  No suspension, very light, very fast and easy to pedal.  Suitable for those looking to race or cover long distances

 MOUNTAIN BIKES
The all purpose bike.  Not so fast on the road, but ideally suited for rough trails.  Knobbly tyres give good grip on muddy surface, tough frames and handlebars, with suspension to smooth the bumps and reduce falls

 TREKKING BIKES
Most suitable for those who will travel mainly on the road but who might venture down the occasional canal path or disused railway track.  Tougher than road bikes, easy to ride

 COMMUTER BIKES
Mainly for utility purposes where comfort, luggage and keeping dry are the most important considerations.  They usually have large wheels for speed, and mudguards to protect against the elements.  Folding bikes also fall into this category, which some call, 'the bike for the car'.