Mold

hollow form or matrix for shaping a fluid or plastic substance

A mold is a hollow shape which can be filled with a liquid which can harden or set and take the shape of the mold.

Bundt-style silicone and metal pans (2008)
Late 19th- and early 20th-century food molds

Molds are used in cooking for jelly and cakes.

One half of a bronze mold for casting a socketed spear head dated to the period 1400-1000 BC. There are no known parallels for this mold.
Stone mold of the Bronze Age used to produce spear tips.
Ancient Greek molds, used to mass-produce clay figurines, 5th/4th century BC. Beside them, the modern casts taken from them. On display in the Ancient Agora Museum in Athens, housed in the Stoa of Attalus.
Ancient wooden molds used for jaggery & sweets, archaeological museum in Jaffna, Sri Lanka.

They are also used in manufacturing, sometimes for very complex things.

See also mould