What is a Fortran unit?

A Fortran program consists of one or more program units. The unit containing the PROGRAM attribute is often called the main program or just main. The main program should begin with the PROGRAM keyword. Unlike some other languages, this keyword for the beginning of the main program unit is not required in Fortran, but its use is highly recommended. Example

PROGRAM myprog
non-executable statements
executable statements
END PROGRAM myprog

Unlike many other programming languages, Fortran is not case-sensitive; that is,

program myprog
Program Myprog
PROGRAM myprog