A cell is an ordered pair of nouns. It is a fundamental data type in both Hoon and Nock: a noun is either an atom or a cell. Its mold in Hoon is ^, and it's formed with either square brackets like [123 456] or :-family runes. A cell can also be thought of as an internal node in the binary tree of a noun. It is similar to a cons-cell in Lisp.
Further Reading
:-family rune reference: The various runes in Hoon that form cells.