When someone declares that a point they or someone else has made is "moot" it means that it is essentially meaningless or irrelevant, often because it has been superseded by subsequent events or information. Other phrases that can be used as synonyms for "moot point" include "arguing over semantics," "irrelevant debate," "empty argument," "academic point," "pointless discussion," "merely theoretical," or "beating a dead horse." These phrases all convey a lack of value or usefulness in continuing to debate a particular topic, either because it has already been settled or because it is simply not worth pursuing any further.