A very small flying insect. The word, used in Matthew 23:24, is a general word for a small fly.
The third plague in Egypt before the exodus consisted of gnats (Exodus 8:16–18; Psalm 105:31). The King James Version translates the Hebrew word as "lice." But, Exodus 8 describes the breeding pattern as insects rising from the dust. This more likely describes gnats rather than lice.
Since “gnat” is a general term, the small flies of that plague may have included several small species such as mosquitos, harvester gnats, midges, or sand flies.
The sand fly has a far more painful bite than the mosquito. Further, it does not make a buzzing noise in flight and is so small that it can pass through most mosquito netting.
Gnats were attracted to wine while it was fermenting. The Pharisees, in particular, would strain their wine to avoid consuming ritually unclean insects (Matthew 23:24).