
On knees and elbows, protecting the neck.
Turtle is when you are curled up on your knees and elbows, usually after escaping a pin or stopping a guard pass. It is a short-term shelter, not a resting place: your back is exposed and your opponent will try to sink hooks or attack your neck.
Keep your elbows tight to your knees and your neck protected, and don't stay still. Roll back into guard, sit out, or come up to a single leg. The longer you stay in turtle, the more chances you give them.