To "veg out" is a slang term referring to relaxation: To engage in something passively, with all the effort of a vegetable.

veg out (phrasal verb): an informal expression meaning to relax by doing something that needs very little effort, for example watching television. 'Laze (around / about) is another expression that can be used to mean 'to relax but without doing anything in particular': 'I’ve spent the afternoon just lazing around.'

It is mainly used to mean 'to sit around and do nothing'

Veg out: Relax in a slothful and mindless manner. Veg out is not a single word, but a phrase and of course derived from the associations of vegetables. Julia Roberts' character in the movie " Pretty Woman" uses it as: "Let's watch old movies all night... we'll just veg out in front of the TV."

Veg = vegetable. I don't know any relaxed vegetables, do you? There is no further slang, we're talking about that phylum and form of life which is not animal. It's an noun, it's not slang, it's abbreviated and that's it. A person can vegetate, which is slang, or a person can be a potato, also slang, but there are many words meaning lazy, and there is new slang every gerneration. Enough for my first free lesson. For the "out" part, tune in next time.