Three accepted meanings:

1 A unit of brightness of nebulae. A nebula is a cloud-like object visible in the night sky, using a telescope or binoculars; think milky squished star. It - a Crab - is, by definition, equal to the brightness of the Crab Nebula, which was seen as a supernova in 1054 A.D., by Chinese and Arab astronomers; also known as the nebula M1 (Messier1).
A Crab has a sub-division millicrab, which any half-competent student of the metric system will be able to tell you is a thousandth-part of a Crab.

2 A hard-shelled crustacean, with a body generally wider than it is long, two pincers, and a wide variation in size, ranging from pea-crabs, about the size of the eponymous vegetable - to spider crabs, which have a claw span of three or four metres/yards in large (= old) specimens.

3 Pubic lice. This indicates that you may not have been too careful aboutyour fuck-buddies.
1 The new nebula is about five hundred and twenty millicrabs - say half the brightness of the Crab Nebula - said the little blonde astronomer; plainly, she didn't seek to sensationalise this new discovery.

2 Crabs can be caught in many coastal waters - but be careful picking them up, as they can nip.

3 'That damned soccer-jock gave me crabs - he must have shagged Brutus last week!' said Pandora with resignation, whilst counting her plentiful takings.
by railtracksurvivor May 01, 2009
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Nasty ass buggers that live in your pubic hairs.
Guess who, the Crabs. Your pubes, we'll grab. We wait on bedsheets and toilet seats, then pinch your nuts, with our feet. The Crabs, oh yes, the Crabs. The Craaaaaaaaabs.
by (name goes here) July 30, 2006
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A sexually transmitted disease contracted through sleeping with the infected. It results in an infestation of pubic lice in your pubic region and it itches so bad you'll wish you were dead.
by Marla Singers vagina December 10, 2009
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def1: infestation of the pubic hair by crab lice
def2: These crustaceans have a hard bony or chitinous outer covering with a small abdomen concealed beneath it, short antennae, and five pairs of legs, of which the anterior pair are large and pincerlike.
crabs of the ocean
crabs in the balls
by http://anserq.net December 31, 2005
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when you are rowing and your shaft gets stuck in the water causing the oar to stay in place. basically get hit by the oar when you catch a crab. Crabs can range from small hits that don't hurt much to an ejection crab were you are shot out of the boat.
Did you see that kid he made his boat lose because he caught a crab

Did you see him catch the ejection crab it shot him straight out of the boat haha
by waaaa man June 02, 2010
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