Froghemoths are a species of monster from the early days of Dungeons & Dragons. They belong to that box full of really weird ideas, like the Flumphs and the Vegepygmies and the Flail Snails and the Gelatinous Cubes, that old-school fans alternatively remember fondly and cringe at, and which every edition seems to try to ignore for as long as possible before bring them back out in a marketing ploy.
Froghemoths originated in the "science-fantasy" module Expedition to the Barrier Peaks, where they were one of the biggest, nastiest critters to come out of the ruined spaceship. A froghemoth is a gigantic monster, something vaguely like a bipedal frog-dragon with three eyes on stalks atop its head and four slimy tentacles in lieu of forelimbs. Mindless monstrosities, their immense size and huge appetites make them extremely dangerous, enough so that they consider giants and dragons to be staple food-sources to hunt.
Despite being out of one of the 1e modules, they're Open Game License, and so Pathfinder gleefully brought them out as part of its Misfit Monsters Redeemed sourcebook. They were also in Dungeon 128, where the players fight one.
Froghemoths reappeared alongside Flail Snails in Volo's Guide to Monsters for Dungeons & Dragons 5th Edition.
Notably, they have some of the weirder elemental power rules in D&D, being immune to electrical damage, but still suffering a variety of penalties whenever subjected to it.