From 1d4chan

Humanoid is a term ubiquitous in both fantasy and science-fiction, meaning "a creature that is similar to a human but not a human". Something with bilateral symmetry, stands upright, two legs, two arms and a head in the right positions and joints in mostly the right places qualifies, even if it has green skin, three eyes and a tail. Unless you're talking about Dungeons & Dragons, in which it case it has some more specific meanings.

In Advanced Dungeons & Dragons, for unknown reasons (possibly due to his belief in the importance of humanocentrism), Gygax divided the various nonhumans into two categories. Anything that was either half-human or had been a protagonist race in The Lord of the Rings was deemed a Demihuman (why gnomes got in on this, who can say, maybe due to their basically being an elf/dwarf crossbreed). Anything else that had a roughly human-like form and some level of civilization was deemed a Humanoid. On paper, this was a neutral term referring to all non-demihuman races, from benevolent-to-neutral ones like centaurs, firbolgs and aarakocra to evil ones like orcs, ogres, goblinoids, gnolls, kobolds, etc. In practice, it was just used as a catch-all phrase for "all the races you are legally allowed to kill in this game". Though in practice demihumans were just labeled as humanoids when types started to be more formally used.

When Dungeons & Dragons 3rd Edition came along, they dropped the usage of demihuman completely and just used humanoid for everything... Okay that's kind of a lie. See in this edition they also decide to make the use of "creature types" to divided up the various creatures of the D&D multiverse standard practice. To accompany this change they decided to add some mechanical weight to Types by having them define the potency of racial hit die, some default immunities, and if certain spells can target the creature. Humanoid became the "normal type" - the races that were fundamentally human-like in nature, being creatures based on relatively normal biology with little in the way of truly powerful inherent magic. If they did posses powerful magic, for example a Medusa, or overtly monstrous behavior and appearance, such as a Minotaur, they were dubbed a Monstrous Humanoid. A Gnoll or Lizardfolk, on the other hand, is just a human-shaped animal, and thusly is a Humanoid type.

In Star Wars humanoid is used to mean a species with two legs, two arms and a head connected to the same torso. Being furry or scaly is no obstacle to being classified as "humanoid", but additional limbs are. Related to humanoid is the "Near-Human" classification, which is applied to species that are immediate off-shoots of humanity. Only near-humans are known to have produced hybrids with humanity.