1. (noun) An amoeba-like protozoon belonging to the class Foraminifera that typically lives inside a test (shell) comprising one or many chambers made from calcium carbonate or sediment particles, and with one or more openings through which the animal can extend a net of pseudopodia for locomotion, to anchor itself, and to capture the bacteria and diatoms on which it feeds. The test may be highly elaborate. Most are smaller than 1 mm across, but the largest, a single cell with many nuclei, is up to 200 mm. Almost all foraminiferans are aquatic and most are marine, living on and in the seafloor sediment, but a few forming part of the plankton. There are about 10,000 extant species and 40,000 known as fossils.

2. (adj.) Pertaining to the Foraminifera.