What is the origin and definition of the expression "caught between a rock and a hard place"? I also heard it in a situation where it could have had a jocose double sense, but I may have misunderstood.
The expression is used when there is a dilemma or only two equally difficult decisions. It can be implied where there is a mandatory to make a choice between at least two unpleasant choices.
The origin, according to Phrases Dictionary, is derived from an economic issue where workers face underpaid wages ( a rock) and unemployment (hard place). The full version of the story can be found in the reference.
Other origin worths mentioned is the Greek mythology "Between Scylla and Charybdis", where Odysseus has to take a route between six-headed monster Scylla and the whirlpool Charybdis. For further reading on Wikipedia.