What is the Full Form of ETA ?

ETA - Estimated Time of Arrival

Estimated Time of Arrival also known as expected time of arrival, is the amount of time remaining for a particular entity to arrive. The entity can be a train, ship, aircraft, a courier, a vehicle or any emergency service. The time can be given in form of a particular date, along with an expected time in hours and minutes. This measurement of time is done with the help of past data or by calculating it with the help of a formula.

For example - Suppose, if an aircraft has to go from city 1 to city 2, with distance between them is 2400 Kms. Now, if the aircraft travels at the rate of 400 kms per hour. The Estimated Time of Arrival (ETA) at city 2 will be 6 hours. We got this number with the help of a formula :
ETA = Total Distance/Speed