3GPP 38.300 v19.3.0 — the document's own text
4.11 Wireless Access Backhaul
Taught in 4. What NR actually is, in the shape its own document gives it (TSG RAN — the group that specifies the radio, overview).
Wireless Access Backhaul (WAB) is supported by means of the WAB-node, which provides NR access links to UEs via a gNB functionality, referred to as the WAB-gNB. The WAB-node further supports a WAB-MT function, which terminates an NR Uu interface to a gNB that is used for the backhauling of the WAB-gNB’s traffic. The WAB-node may be stationary or mobile.
Further details of WAB are defined in TS 23.501 [3] and TS 38.401 [4].