The Collaborative International Dictionary
Heterogamy \Het`er*og"a*my\, n. [See Heterogamous.]
(Bot.) The process of fertilization in plants by an indirect or circuitous method; -- opposed to orthogamy.
(Biol.) That form of alternate generation in which two kinds of sexual generation, or a sexual and a parthenogenetic generation, alternate; -- in distinction from metagenesis, where sexual and asexual generations alternate.
--Claus & Sedgwick.
Wiktionary
n. 1 (label en biology) The state of conjugating gametes that are different in size, structure and function 2 (label en sociology) marriage or similar union between people of different sexes, or social stratum, such as races(,).
Wikipedia
Heterogamy (from Ancient Greek ἕτερος heteros, "other, another" and γάμος gámos, "marriage") has a number of biological definitions.