3GPP 23.501 v20.2.0 — the document's own text

5.9.2a Subscription Concealed Identifier

Taught in 7. Every name the system uses (The 5G system architecture, in depth), 4. Knowing who you are and where you are (The 5G system architecture, overview).

The Subscription Concealed Identifier (SUCI) is a privacy preserving identifier containing the concealed SUPI. It is specified in TS 33.501 [29].

The usage of SUCI for W-5GAN access is further specified in TS 23.316 [84].