A gecko is a small or medium-sized lizard of the family Gekkonidae, part of the reptile class. Geckos live in warm areas of the world, most usually in or around the houses of humans. Geckos apparently lack movable eyelids, which must make it difficult for them to catch a bit of shut-eye, poor things. They have pads on their feet with backwards-pointing hooky things (ingenious fibres, corrects TheLady, and who am I to argue?), that allow them to cling to apparently smooth surfaces and run around on ceilings, chasing after the insects that are their chief prey.
My cat in Thailand would always scan the areas near the door when he came in, checking if there was a gecko close enough for him to grab as a snack. If there was, he'd jump for it, though more often than not he would only succeed in dislodging a tail, which would flop disconcertingly around on the floor until he ate it. The now-tailless gecko would sport a stump for a few days which would blossom over a few weeks into another tail just like the lost one.
Geckos differ from lizards in that they have voices, each of the 300 species making their own unique sound. By far the most unusual in my not-inconsiderable experience in the tropics is the Thai gecko known as a tookay. These are relatively large - maybe up to a foot in length - specimens with a weird gray squishy look to them. They live outside front doors on porches and balconies. At night this gecko builds up into a large crescendo of sound, letting out a string of tookay cries - up on the took, down on the kay - that will go on perhaps a dozen times, finally ending with a defeated and exhausted-sounding groan. Thai people, always superstitious, count the number of cries, and say that an even number means bad luck. Tookays, once heard, are never forgotten, and if those of us who had heard it were gathered together, our voices would unite in the battle cry of the mighty tookay, squashy gecko warrior of Southeast Asia.