OCPP is an open standard maintained by the Open Charge Alliance. It defines how chargers communicate with a central management system for functions like starting and stopping sessions, authorisation, metering, remote diagnostics and firmware updates. OCPP 1.6 and 2.0.1 are the most widely used versions.
OCPP compliance protects owners and operators from vendor lock-in, because chargers from different brands can be managed by the same software and the software provider can be changed without replacing hardware.