A compiler is system software (a set of a computer program) that converts source code written in a programming language (source language, usually HLL) into another computer language (target language). It processes every statement written in a particular programming language and turns them to machine language. After writing the program the programmer runs the code in an appropriate language compiler specifying the name of the file that contains the source statements.
When executing or running the program, the first task of the compiler is to parse all the language statement syntactically one after another and then build the .obj file and finally build the executable file (which is possible if the final code is correct). The output of the compiled code is referred to as the object code or sometimes called the object module. (It is to be noted that this object file/object module is not related to OOP).