The operational definition of happiness is when a person can identify one or more specific, observable events or conditions that any other researcher can independently measure or test for them when relating to happiness.
For example, happiness can be measured in an individual by the amount of times a person laughs during a conversation. An observer is able to count the laughs in a specific setting. Based on the number range that observer has which determines happiness, they're able to make a decision. It's important to keep in mind, however, that these observations and measurements alone don't signify if the subject is actually happy.