OpenSSH 8.0 released

Quoth the man page:

"A trailing slash on the source changes this behavior to avoid creating an additional directory level at the destination. You can think of a trailing / on a source as meaning 'copy the contents of this directory' as opposed to 'copy the directory by name', but in both cases the attributes of the containing directory are transferred to the containing directory on the destination"

(And for the reverse: just searching for "trailing" or "trailing slash" clears that part up pretty quickly).

Rsync's man page may be daunting, but it is extremely well written.

"If all else fails, read the instructions"