Technically, an Artifical Intelligence (or A.I.) is the « construction of computing programs doing tasks usually reserved tu humans bacause they’re necessitating very complex mental process ».
In science fiction, an A.I. designates an artificial creature provided with enough computing power to seem “intelligent”, able to proceed to mental feat out of other machines range. This intelligence can also come from interaction of a lot of computer connected in network.
Generally, an A.I. is a huge machinery (even planetary) and fixed (unlike a robot) but, in some works, they can take any forms, any scale and any means of transport that their author’s imagination can provide.