No, a STEM is not inherently a tomboy. The term "STEM" in this context likely refers to a specific type of lesbian identity, not a descriptor of a personality or style like "tomboy." While some individuals who identify as STEM might exhibit traits associated with tomboys, it's not a defining characteristic.
Several sources mention "STEM" in relation to lesbian identities, often contrasting it with terms like "stud" and "femme." One source indicates a STEM might lean more towards the femme aspect, while others show that a STEM can be seen as a mix of masculine and feminine characteristics. Crucially, none of these sources define a STEM as a tomboy.
The provided links mostly concern a bicycle stem called "Tomboy," highlighting the potential for confusion between the unrelated terms. The links are entirely focused on bicycle components and not on social identity.
A tomboy is typically defined by a girl or woman who enjoys activities and behaviors traditionally associated with boys. A STEM, as a descriptor of a lesbian identity, is related to a spectrum of presentation and self-expression within the lesbian community and doesn't directly relate to this traditional definition of "tomboy."
In short: While there might be overlap in certain characteristics, a STEM is not synonymous with a tomboy. The terms represent distinct concepts.