With regard to bicycles, the fork is the device which connects the handlebars to the front wheel. For such a simple device, forks come in many, many different forms and are integral to the handling and overall 'feel' of the bike.
Touring bikes and consumer gear will often have a bent fork, sloping away from the rider. This has the effect of dampening road vibration by allowing a fair amount of flex up and down that is not directly transferred to the rider's hands.
Racing bikes, especially those designed for sprinting, will often have straighter or straight forks, this allows the most direct transfer of power and the best handling, although the rider will feel each and every bump in the road below him.
The material of the fork is also important, with steel and carbon fibre both being popular for their 'comfort' as well as good power transfer. Steel is less popular as it is much heavier and isn't as stiff as the alternatives. Aluminium is popular where performance is more important then comfort, as it is fairly stiff, and where carbon fibre may be too expensive.