A child process is a computer process created by another process (the parent process).
A child process inherits most of its attributes, such as open files, from its parent. In Unix-like OSes, as Linux, a child process is in fact created (using fork) as a copy of the parent. The child process can then overlay itself with a different program (using exec as required.
Each process may create many child processes but will have only one parent process, except for the very first process which has no parent. The first process, called init in UNIX, is started by the kernel at booting time and never terminates.