(grammar) A pronoun that introduces a relative clause and refers to an antecedent. Some words that can be used as interrogative pronouns can alternatively be used as relative pronouns: what, which, who, and whom. The other relative pronouns are whoever, whomever, whatever, and that.

(sciences) A measure of the density of a material. The ratio of the density of a substance to the density of water at the same temperature. It is dimensionless and therefore has no units.

(grammar) A subordinate clause that modifies a noun.

(grammar) the superlative (a degree of comparison) when it is used to express the highest degree of something in relation to something else

(topology) subspace topology

plural of relative pin

(chess) A pin in which moving away the pinned piece would allow capture of a piece other than the king.

(physics, meteorology) Synonym of gauge pressure

plural of non-relative

(statistics) The number of data points satisfying something divided by the total number of data points.