The ochre jelly is a slimy monster that appears in NetHack.
Ochre jellies attack by engulfing, and have a dangerous passive acid splash when attacked in melee. They can corrode iron or copper objects with their passive attack: a 1-in-6 chance of damaging vulnerable objects used in melee or from range, and an independent 1-in-2 chance of splashing back acid in melee that in turn has a 1-in-30 chance of eroding a single piece of worn armor except for boots. The engulfing attack does not corrode objects, despite being acidic.
Ochre jellies are quite slow, so you can easily run away if you aren't prepared to handle them. Their passive acid attack does a fixed 3d6 damage, as opposed to the (level+1)d6 that one finds on monsters such as spotted and blue jellies.
In SLASH'EM, the engulfing attack can now corrode objects in open inventory, including your alignment key.