the practice of inserting obscure pop-culture references or quotes (sans footnotes) in casual conversation in order to (implicitly) connect with those who understand that reference.
(M is about to leave a party, saying goodbye to P)
M: See you guys. Thanks for all the fish.
(referencing Douglas Adams' The Hitchhiker's Guide to the Galaxy - M is brocasting in a subtle manner)
P: So long, and thanks for all the fish.
(P is thereby completing the quote, thus indicating that he is also familiar with the reference. P has successfully received the brocast)