We had a frogfish-tastic week in Lembeh but what is a frogfish?

This week we had a Frogfish-tastic week in Lembeh with lots of different species: Hairy, Giant, Painted, Warty / Clown, all of varying colours and sizes. PLUS we found three Sargassum frogfish when cleaning our beach in front of the resort! But what are these weird fish?