Hilariously mangled spelling of "Gorn", the large reptilian alien from the Star Trek television series.
Gorn was first misspelled as "Gorm" in various forum and email messages, which was later further mangled into "Grom".
Fun Fact: Groms is generally considered to be the singular of Groms.
Why'd you choose the Groms?" "Oh, you know, beacuase I like scaley lizards
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