What is "high-functioning?"

When an autistic person is described as "high-functioning", what does this really mean? It's effectively a measurement of how close to "normal" that person appears on the outside, how indistinguishable from their peers they can manage to appear.

The word does nothing to offer insight into the person being described.

It is certainly not a measure of even how autistic they are, but rather, describes only how well that person can pretend to be like non-autistic people.

Please avoid using high and low functioning labels, as they dehumanise by generalising, and perpetuate negative stereotypes about autistic people, and offer no insight into the person being described.