I despise when reviewers use those words in describing a piece of equipment unless they were, quite literally, at the recording. Once those words are used, I pretty much stop reading since IMO the reviewer is full of BS.
If they compared the input (recording) to the output from a speaker or amp, like with a graph, then it can make sense.
Otherwise it is hyperbole when used subjectively..
If the step function, or impulse response, of the speaker is not textbook, then it is hard to claim it is faithful.