Is the api core group subset of the Kubernetes APIs, or is it like a wildcard that covers all APIs when used in rules?

In this training session,  When Nigel defined the ClusterRole under rules there was this:

rules  
 - apiGroups: [""]

is  that same as:

rules  
 - apiGroups: ["*"]

does [""] that means core api/legacy group covers all other api groups?

P.S: forum topic tags/labels still does not cover Kubernetes topics