It refers to the “normal” motions that populate the repertoire of each and every person on the planet. We can’t even begin to read someone until we first have their baseline pegged.
For example, to read someone that is normally flighty and constantly moving as agitated, is wrong since they are merely acting out their particular “idiosyncratic nonverbal behaviour.” That is, the body language that is particular to specific people and that makes up their repertoire, or basket of cues, considered normal for them.
The more cues that appear in association with other cues, the more accurate one can be about the underlying meaning.
It isn’t impossible to see cue clusters in the six’s and sevens or higher.
By establishing a baseline it will be possible to catch sudden changes in body language.