A Bluetooth profile (mode) designed to enable a two-way wireless headset to be used with a Bluetooth phone.
Headset is one of the most common Bluetooth profiles. Nearly all phones support it, although some phones only support the very similar Handsfree profile (HFP), which can also be used for headsets.
A newer profile called TMAP (Telephony and Media Audio Profile) is designed to replace HSP. TMAP is part of LE Audio, the newer standard for all kinds of audio over Bluetooth.
See: LE Audio
Headset Profile supports simultaneous two-way (full-duplex) audio, but it does not support stereo audio.
HSP can be used with devices other than phones. For example, a Bluetooth headset could be used with a Bluetooth-enabled PC and VoIP software to place an Internet phone call.