The explanation is:
"-R, --recursive
operate on files and directories recursively"
What does "recursive" mean here?
"Recursive" implies that the operation will be performed for all files and directories (and all files and directories within any directory). So
chown -R foo /some/path
would change file owner to foo
for all files and directories in /some/path
p.s. You might have even seen the dictionary entry for recursive
:
recursive, n: See recursive