The execve() system call is used by the Unix loader to load and execute a new program in place of the current process. The execve() system call is part of the exec family of functions in Unix-like systems (execve, execv, execvp, etc.).
Before the loader performs its tasks, the fork() system call might be used to create a new process (child process) if necessary. However, it’s the execve() call that triggers the actual loading and execution of a new program.