There is a celebrated definition of "bullshit" by the philosopher Harry
Frankfurt, which is basically a disregard for whether what one is saying
is true or not, as opposed to lying, when one knows it isn't true and is
deliberately recounting a falsehood.
...Davis [Evan
Davis, author of
Post-Truth: Why We Have Reached Peak
Bullshit and What We Can Do About It] wants to define bullshit much
more broadly, as "any form of communication -- verbal or non-verbal --
that is not the clearest or most succinct statement of the sincere and
reasonably held beliefs of the communicator". In that case, we all
traffic in bullshit most of the time, and for very good reasons.
"Genuine frankness is not the norm but the exception,"
Davis points out, defending the circumlocutory speech of diplomats or
doctors, of people offering sympathy or encouragement, and even of
politicians in some circumstances. At one point, amusingly, he even
defends a piece of flowery wine writing. "This is good gibberish," he
judges, "because I think for the intended readers the material is well
devised."