Twitter @ and d messages - who can see what?
Since I seem to explain this several times a month, I thought it was worth putting together a print-out-and-keep chart to help make it clearer.
Best viewed large.
LATER: Updated to reflect differences to public and private accounts, and other reply oddities, plus make notes easier to read.
If you like this you might also like the anatomy of a hashtag I did a while back.