What type of clause is underlined in this sentence?
“Do not talk to mom until she has had her first cup of coffee.”

A subordinate clause is a clause that cannot stand alone as a complete sentence because it does not express a complete thought. It depends on the main clause to provide a complete meaning. In this case, "until she has had her first cup of coffee" is a subordinate clause because it provides additional information about when the action of not talking to mom applies. The main clause in this sentence is "Do not talk to mom."