P-relation See RM/T.
pair Either a set of cardinality two or, more usually, an ordered pair (q.v.), as the context demands.
parameter A formal operand in terms of which some operator is defined, to be replaced by some argument when the operator in question is invoked. Simplifying slightly (see generic operator), every parameter is declared to be of some type, and any argument corresponding to a given parameter is required to be of the same type as that parameter. Contrast argument.
parent / parent table Deprecated, because inappropriate, terms sometimes used in SQL contexts to mean (the SQL analog of) a referenced relvar, q.v.
partial function Let f be a function with domain d and let dd be a superset of d; then f can be regarded as ...