from
The Free On-line Dictionary of Computing (8 July 2008)
sum of products
1. <mathematics, logic> Any mathematical {expression} in which
an addition operator is applied to two or more subexpressions
each of which is an application of a multiplication operator.
The most common case would be scalar addition and
multiplication, e.g.
ab + cd
but the term is used for other kinds of operators with similar
properties, such as AND and OR in {Boolean algebra}, e.g.
(a AND b) OR (c AND d)
2. <types> {algebraic data type}.
(2008-02-04)