noun
(uncountable, informal) Nonsense; drivel; idle, meaningless talk.
(informal, in the plural, the blahs) A general or ambiguous feeling of discomfort, dissatisfaction, uneasiness, boredom, mild depression, etc.
(informal, derogatory) A fool, an idiot.
adjective
(informal) Dull; uninteresting; insipid.
(informal) Low in spirit or health; down.
interjection
An expression of mild frustration.
(When spoken repeatedly, often three times in succession: blah blah blah!) Imitative of idle, meaningless talk; used sometimes in a slightly derogatory manner to mock or downplay another's words, or to show disinterest in a diatribe, rant, instructions, unsolicited advice, parenting, etc. Also used when recalling and retelling another's words, as a substitute for the portions of the speech deemed irrelevant.
Representing the sound of vomiting.
verb
(intransitive) To utter idle, meaningless talk.