vCenter Service overall health changed from 'green' to 'red

I received this alarm as datacenter target but how can I know more details?

I don't understand what means OR in the alarm definition because there are twice RED status, 1 GREEN status and 1 YELLOW status

ALARM:

Target: Datacenters

Previous Status: Green

New Status: Red

Alarm Definition:

([Event alarm expression: vCenter Service Overall Health Changed; Status = Red] OR

[Event alarm expression: vCenter Service Overall Health Changed; Status = Green] OR

[Event alarm expression: vCenter Service Overall Health Changed; Status = Red] OR

[Event alarm expression: vCenter Service Overall Health Changed; Status = Yellow])

Event details:

vCenter Service overall health changed from 'green' to 'red'