Another class of repeaters do not simultaneously retransmit a signal, on different frequency, as they receive it. Instead, they operate in a store-and-forward manner, by receiving and then retransmitting on the same frequency after a short delay.
These systems may not be legally classified as “repeaters”, depending on the definition set by a country’s regulator. For example, in the US, the FCC defines a repeater as an “amateur station that simultaneously retransmits the transmission of another amateur station on a different channel or channels.” (CFR 47 97.205(b)) Store-and-forward systems neither retransmit simultaneously, nor use a different channel. Thus, they must be operated under different rules than more conventional repeaters.
A type of system known as a simplex repeater uses a single transceiver and a short-duration voice recorder, which records whatever the receiver picks up for a set length of time (usually 30 seconds or less), then plays back the recording over the transmitter on the same frequency. A common name is a “parrot” repeater.