Cats have expressive body language, which is helpful since they lack the articulation necessary to communicate through speech or sign language. Cat postures can express multiple moods and modes, though, and crouching can be especially ambiguous. Your crouching cat may be primed to pounce, fight, acquiesce or rest.
The Stalker Cat Crouch
Is your cat wiggling into a crouch or slinking low to the ground? Are his eyes narrowed and his butt up in the air? Is his tail flicking back and forth and back and forth (and back and forth)? He's probably stalking prey.
Your cat coils and creeps when he's on the prowl. Crouching keeps his muscles taut and ready for sudden swift strikes. You may not see the target -- it could be a bug he sees, another cat he hears, a rodent he smells or your feet, to which any of those senses may apply -- but he's preparing an attack.
The Wary Cat Crouch
Is your cat crouching low to the ground? Are his eyes wide and his pupils dilated? Is his back arched and his tail erect? He's likely feeling fearful or defensive.
When your cat crouches warily he may be bracing for a fight or flight. It's not unusual for cats in this position to move sideways, perpendicular from a threat. It makes him look larger and gets him one step closer to a quick escape or flanking attack.
The Submissive Cat Crouch
Is your cat crouching on an even keel? Is he avoiding eye contact? Are his ears back and is his tail tucked between his legs? He's probably showing submissiveness.
If your cat crouches this way, he may be trying to avoid a fight with another animal by showing deference and capitulation. This crouch makes him look smaller and less threatening to a potential foe. He may even lie on his back, belly up, as if to expose his organs as an act of contrition.
The Plain Old Cat Crouch
Is your cat just crouching? Like, nothing else is happening other than that the cat is crouching? And maybe he closes his eyes and even falls asleep? He's probably resting.
If your cat was an electronic device, crouching would be the position he assumed after a factory reset. Crouching is a normal way for your cat to relax. The position allows him to be more alert than when he lies down, but less alert than when he stands. It's the best of both worlds, at least for cats.