My flight was delayed due to a "tail swap" at the destination airport (the airport I will be flying into). Does that mean anything specific? If so, what is it?
Aircraft are scheduled by some airlines based on "tail numbers", which is the registration of the aircraft, which is displayed on the aircraft either on or (normally) below/slightly in front of the tail. For larger planes in the US, these numbers start with the letter "N", and then are normally followed with 3 numbers and 2 letters. eg, N182UA.
A "Tail swap", "aircraft swap" or "aircraft substitution" is where the plane that is expected to fly a specific flight is changed to a different plane. ie, the "tail number" for the flight is swapped with a different one.
There could be any number of reasons for such a change. It could be that the plane that was planned to fly that route was broken, or that it was delayed by an earlier problem (mechanical, weather, crew, or anything else). Or it might be completely unrelated to that specific plane and they are shuffling planes due to an unrelated issue elsewhere in the system.
Other than the potential for your flight being delayed as a result of the swap (or more likely, whatever caused the swap to occur) - which seems to be what's happened here - the primary impact of an aircraft swap is if they swap in a different type of plane, which will normally have a different seat map/capacity. This may require them to re-issue boarding passed for at least some passengers, and in a worst-case scenario could result in some people having to take another flight if the new aircraft doesn't have sufficient capacity. Normally this will not be an issue as they will normally swap in the same type of aircraft, but sometimes they don't have any similar planes available and have to use a different type.
Best I can find on the subject is that they are swapping an aircraft. Now this makes sense for a departure airport but for the destination it only makes sense if the aircraft is being used as a shuttle between the 2 like NYC - BOS or NYC - Washington