CHUG is an acronym for Classics, Henkei, Universe, Generations. They're the official line of G1-inspired mainline retail toy Hasbro and Takara have been releasing since, what, '06? It includes sub-lines like Reveal the Shield, Combiner Wars, and Titans Return. While the term has been used to describe 3P figures that were always meant to go with official CHUGs, it's often used pejoratively to describe any figure that the speaker feels is lacking some arbitrary quality to be MP enough for them. Ex- "I hope someone else makes an MP Brawn. Brawny is too chuggish, there's like no paint on him."