An enhanced humanoid was any humanoid that received any type of enhancements to their natural appearance or abilities. The most common form of enhancements were eugenics, including genetic enhancements, and cybernetic or cyborg enhancements.
On Earth during the 20th century, ambitious scientists established a eugenics program that created the Augments. (ENT: "Borderland", "Cold Station 12", "The Augments", "Divergence"; TOS: "Space Seed", etc.) Julian Bashir also had a genetically-enhanced background. (DS9: "Doctor Bashir, I Presume", "Statistical Probabilities", "Inquisition", "Chrysalis", "Inter Arma Enim Silent Leges")
Many Suliban were genetically enhanced, including the ability to take any form and enhanced vision. (ENT: "Broken Bow", "Cold Front", "Detained", "Two Days and Two Nights")
Upon discovering the alien differences of Jonathan Archer and Malcolm Reed, members of Gosis' species believed them to be genetically-enhanced soldiers. (ENT: "The Communicator")
Starfleet Admiral Maxwell Forrest believed the newly-discovered Borg to be "humanoids enhanced with technology." Doctor Phlox later noted that "their physical strength has been enhanced." (ENT: "Regeneration") Q later reiterated that fact, describing them as "enhanced humanoids". (TNG: "Q Who") Likewise, Neelix once claimed that, regarding One's inquiry regarding knowing more about the Borg, "Oh, what's to tell? You've seen one cybernetically enhanced species, you've seen them all." (VOY: "Drone")
Doctor Phlox noted that the Xindi-Reptilians were "surgically enhanced, if you can call it an enhancement," upon determining that they had a "suicide gland". (ENT: "Rajiin")
Doctor Bashir noted that the biomolecular diffusion gradient of the (yet unknown) Jem'Hadar youth he was caring for suggested that "his cellular mitosis has been artificially enhanced." (DS9: "The Abandoned")