5G NG Identities (UE and Network Identifiers)

C-RNTI: This is a unique identification, which is used as an identifier of the RRC Connection and for scheduling purposes
Temporary C-RNTI: This identification used for the random access procedure, Random value for contention resolution: during some transient states, the UE is temporarily identified with a random value used for contention resolution purposes
Multi C-RNTI: In Dual Connectivity case, two C-RNTIs are independently allocated to the UE: one for MCG(Master Cell Group), and one for SCG (Slave Cell Group)
Xx-RNTI: This unique identification used to identify the UE context for RRC_INACTIVE

The following identities are used in NG-RAN for identifying a specific network entity

AMF Identifier (AMF ID): It is used to identify an AMF (Access and Mobility Management Function)
NR Cell Global Identifier (NCGI): It is used to identify NR cells globally. The NCGI is constructed from the PLMN identity the cell belongs to and the NR Cell Identity (NCI) of the cell. It can be assumed equivalent to CGI in LTE system
gNB Identifier (gNB ID): It is used to identify gNBs within a PLMN. The gNB ID is contained within the NCI of its cells.
Global gNB ID: used to identify gNBs globally. The Global gNB ID is constructed from the PLMN identity the gNB belongs to and the gNB ID. The MCC and MNC are the same as included in the NCGI.
Tracking Area identity (TAI): It is used to identify tracking areas. The TAI is constructed from the PLMN identity the tracking area belongs to and the TAC (Tracking Area Code) of the Tracking Area.
Single Network Slice Selection Assistance information (S-NSSAI): It identifies a network slice.

Reference: 3GPP TS 38.300 (2017-09) NR and NG-RAN Overall Description; Stage 2 (Release 15)