Imperative programming is a programming paradigm in which statements are written to change the state of the program. This concept emerged at the beginning of computing and is very close to the computer's internal structure. The program is a set of instructions that is run on the processing unit, and it changes the state (which is stored as variables in the memory) in an imperative manner. The name imperative implies the fact that the instructions that are executed dictate how the program operates.
Most of the most popular programming languages today are based, more or less, on the imperative paradigm. The best example of a mainly imperative language is C.