5G Events are described in 3GPP 38.331 section 5.5.4

Event Name Meaning
A1 Server is better than threshold
A2 Server is worse than threshold
A3 Neighbour is better by offset compared to PScell
A4 Neighbour is better than threshold
A5 PSCell is worse than threshold and Neighbour is better than threshold
A6 Neighbour is better by offset compared to Secondary serving cell