DNN: Data Network Name. This is similar to APN in 4G.
Each S-NSSAI may be served by different DNN.
SUCI: Subscription Concealed Identifier.
In 4G, IMSI was provided to the network as a simple text and hackers can easily hack it. 5G addresses this concern and conceals the IMSI (SUPI in 5G) before sending it to the network.
SUPI: Subscription Permanent Identifier Similar to IMSI in 4G. Valid in 3GPP system and is provisioned in UDM/UDR.
PEI: Permanent Equipment Identifier. Similar to IMEI in 4G.