General liability covers injuries and property damage: a client trips in your office, or your crew damages a customer's floor. Professional liability covers financial loss from your work itself: the advice was wrong, the design had an error, the deadline was missed.
Service businesses usually need both, because a single incident can produce both kinds of claim. We place them with the same carrier when possible so there is no argument about which policy responds.
This article is general information, not advice about your policy. Coverage depends on the policy and carrier. Questions? Call 708-303-6666.