QRZ, often pronounced as Q R Zed, is an acronym which means, "Who is calling me?" You will often hear it during amateur radio contests, where a station that has finished a contact will end with QRZ to indicate they are ready to have a contact with a new station.
For example, if K8AMH is involved in a contest wherein he announces his call sign in hopes someone will come back, and another station contacts him as part of the contest, at the conclusion K8AMH might say, "Thanks for the contact, and good luck in the contest. This is K8AMH, <name of amateur radio contest>, Q R Zed." At that point he would stop transmitting and listen for anyone to give their amateur radio call sign.