Roger (Roger That, Roger Wilco)

What do the expressions Roger, Roger That, and Roger Wilco mean?

Definition: I have received your message (and will comply—”wilco”).

Example: “Did you get my email this morning?” —”Yes. Roger wilco. Sorry I didn’t have time to respond.”

Note: These expressions come from military radio (where “roger” is used for the letter R), but are used beyond that context.