3.2.1 Abbreviated terms from IEC 61784-3

CRCCyclic Redundancy Check
PDUProtocol Data Unit[ISO/IEC 7498‑1]
PLPerformance Level[ISO 13849‑1]
PLCProgrammable Logic Controller
SCLSafety Communication Layer
SILsafety integrity level[IEC 61508‑4]
SPDUSafety PDU, Safety Protocol Data Unit