Well, first of all, a pokemon is a creature that can be captured, won(at battles), or bought to be trained as a guardian, pet, or a companion. It can also be used for competitive purposes i.e competing in battles, displaying in a beauty contest (on rare occasions).
The word Pokemon is pronounced POH-KAY-MON (same for plural). It means Pocket Monster. The reason for that is pokemon catchers, called trainers, capture and carry the pokemon with pokeballs. Trainers use captured pokemon to battle wild pokemon for capture. They also battle other trainer's pokemon at places called gyms. If a trainer successfully defeats a gym leader (the head person of the locale gym), they get a trainers' badge. For more detailed information, visit my friend, Pikachu45. He has a great detailed description of a pokemon.
