I'm guessing it's something like MongoDB TTL index[0]. It's useful for huge append-only tables where you want a row to be automatically removed after a period of time. The postgres approach is usually to partition your table by the event/insertion timestamp, and use something like pg_partman[1] to automatically drop entire partitions over time.

[0] https://www.mongodb.com/docs/manual/core/index-ttl/

[1] https://github.com/pgpartman/pg_partman