A "Humanoid" (plural "Humanoids") is a character, male or female, who has a physical resemblance to a human being. They might have a few notable strange things, like multiple eyes and extra limbs, but for the most part they resemble a human being.
A notable humanoid is Wander, who is one of the main protagonists of the series. Another notable humanoid is Lord Hater who is the main antagonist.
One rule always applies to the humanoid body structure: it looks similar to a human for the most part, with a few differences that range from minor to major.