A spider strainer is a low, shallow, round basket on a handle. It is called “spider” because it looks a bit like a metal spider web.
The basket can be made of brass or stainless-steel wire.
The handles were typically made of bamboo or wood, but plastic and metal handles are commonly found now.
A small-sized basket may be 10 to 12 cm wide (about 4 to 5 inches), and about 25 cm long (about 10 inches). Large ones will likely have a 25 cm (10 inch) basket attached to a 33 cm long (13 inch) handle. Typically the baskets have no hooks for hanging or other extraneous appendages (the holes for hanging will be in the handles, or be loops attached to the ends of the handles.)
Spider strainers are used in Asian cooking for stir-frying in woks, and deep-frying.
The clean-line design of the basket allows it to be used with great efficiency in Western cooking as well, for example when scooping pieces of vegetable or fruit out of a blanching pot. It is able to move without interference along the inner bottom edges of pots to chase down random stray pieces of food.
For the same reason, some people say spider strainers make the best kitty-litter scoops.