Involving four elements.

A serving of four shots of espresso. / (chess) A kind of round-robin tournament between four players, where each participant plays every other participant once.

Having four shots of espresso.

(informal) A quadrangle (quadrangular courtyard). / (informal) A quadruplet (infant). / (informal, computer graphics) A quadrilateral. / (informal) The quadriceps muscle.

(poker slang) Of or relating to quads.

(transitive)

A quad bike (from quadricycle) / Abbreviation of quadrillion BTU. (10¹⁵ BTU)

to ride a quad bike

(letterpress typography) A blank metal block used to fill short lines of type. / (printing slang) A joke used to fill long days of setting type.

(letterpress typography, transitive, intransitive) To fill spaces in a line of type with quads. Also quad out.