“Some of this process of looking things up and finding the corresponding sequences of machine language can be done before the program is executed. This saves time, because if the program is going to be executed more than once, there’s no point in looking up the same things over and over again. When most of the work of conversion is done beforehand, the translation process is called compilation, and the program that performs the compilation is called a compiler. If most of the work is done while the program is being executed, then the process is called interpretation, and the program is called an interpreter. There is no hard and fast line between the two.”