The correct answer is - gap.
A seismic gap, is the time period between an earthquake that has happened in the past, and an earthquake that will happen in the future. The seismic gap can vary greatly, and it can be a period of only few months, or it can be as long as few decades or centuries.
For example, on the Greek island of Crete, a typical seismic gap is a period of few weeks, and this is because the island is right next to the plate boundary of Eurasia and Africa. On the other hand, just north, in the capital of the Republic of Macedonia, Skopje, the seismic gap between the devastating earthquake of 1963, and the next similar earthquake in 2016, took 53 years.
