First, here is the javax.validation javadoc
When you want to validate a bean, you actually call Validator.validate(T object, java.lang.Class… groups)
It will then check the validations constraints of the specified groups. It allows to use several validation cases.
What you describe in your question is accurate.
Note, if you do not put any group on your constraints, then the constraints belong to the default group, which is the only validated group if you don’t specify any group when calling validate(T object).