A "welcome cocktail" refers to a drink that is offered to guests upon arrival at a social gathering or event. It is a gesture of hospitality and serves as a way to greet and make people feel welcomed. Full definition
When we arrived, the hotel provided us with complimentary welcome cocktails at the restaurant overlooking the ocean. (hannahshelby.com)
How refreshing to arrive at a resort, receive welcome cocktails on arrival and get to jump into a pool you have all to yourself. (wildjunketmagazine.com)