There are some words that are already used by FORTRAN programming Language to define the syntax for the code. Such words are reserved words.
Reserved words in FORTRAN cannot be used in variable name or program name.
Some text editor offers syntax highlighting. So, the reserved words also might get highlighted in different colors.
Below are the reserved words:
if, program,end, then, else, elif, select, case, data, array, sum, size, kind, huge, do, goto, print, write, read, open, close