A genre of popular furry character in Japan, literally being an abbreviation of chibi and kemono.
Not all chibi furries are chibikemo - chibikemo characters are designed with very small proportions even by chibi standards, usually fitting into the archetype of "TDM" (a mascot character who is 2-3 heads tall).
Chibikemo characters often have big eyes, are primarily animal-shaped despite their bipedal stance and anthropomorphic behavior (often being digitigrade), and are frequently fantasy creatures.
Chibi itself might not always apply, depending on the proportions of the character.