Back and Back when

Back adverb - Earlier than the present time.

Back when and back are semantically related In some cases you can use "Back when" instead an adverb "Back".

Nearby Words: backward, backing, backed, backside, backwards

Back and back when are semantically related in earlier topic. You can use "Back" instead an adverb phrase "Back when", if it concerns topics such as in the past, previously in time or order.