3GPP 24.501 v20.0.0 — the document's own text
8.3.9.7 Mapped EPS bearer contexts
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
This IE is included when interworking with EPS is supported for the PDU session and the mapped EPS bearer contexts is modified.