An anchor is a point of reference that can be formed even without a person's knowledge and influences his or her decision.

Everyone has their specific reference points from which they evaluate the world (e.g. if they want to buy or assess something). These do not have to be irrefutable, but can change according to the information (which is not necessarily correct or suitable). They are formed consciously, but also through unconscious influencing.

For example, if a seller names a price that is much higher than the one that the buyer has in mind. This creates a new reference point in it. The seller then goes down with his price. However, this is still higher than the one that the buyer originally had in mind. However, he now believes he has made a bargain because he sees this price not from his original point of reference, but from the one that the seller named first.

Or another example: you assess a person in another way, and the sudden change  (see above) suddenly changes the anchor.

The anchor is a judgment heuristic. This means that certain triggers or facts lead to a relatively quick judgment that has not been thought through thoroughly.

The difference between anchor and midpoint is:

The anchor is a point of reference from which one consciously or unconsciously evaluates something. This can change, and the ratings change accordingly

A midpoint is a neural network that wants to fulfil an aim. It uses everything that is useful for this and everything else decreases in influence and value.