What does the term master$-$slave mean?

A particular implementation that uses two gated latches in such a way that the flip$-$flop outputs only change on the clock edge. If the inputs to the flip$-$flop need to be unstable for a short period of time around the clock edge. $$ If the inputs to the flip$-$flop only need to be stable for a short period of time around the clock edge. A flip$-$flop where the flip$-$flop outputs only change on the clock edge.