What is a simile?

Similes:

“their sleeves, inside their coats, over their shoulders and out, so they could leave their woolen fingers dangling, like a spare pair of hands, like a scarecrow”.

“the thing came into view – its head, which was triangular, appeared like a rubbery or fleshy mask over a shapeless sprouting bulb of a head, like a monstrous turnip; its large body appeared to be glued together, like still wet papier-mache, or the carapace of stones and straws and twigs worn by caddis flies underwater”..