Interleave will take two to four image sequences and interleave them. The resulting image sequence will have the same start frame as the first of the inputs. The additional inputs will be trimmed to match the first input. The resulting sequence will be the total length of all the inputs, after trimming.
For example, if you have two inputs, one ABCDE and the other 12345, the result of interleave will be A1B2C3D4E5.
This is useful to prepare sequences for the Mosaic COP.