What is strong suit?

The term "strong suit" generally refers to an area of personal strength or expertise. It originally comes from card games like bridge, where a "suit" refers to one of the categories of cards (hearts, diamonds, clubs, spades). In this context, a "strong suit" would mean the suit a player has the most cards in or the highest-ranking cards. Over time, the expression broadened in use and now commonly denotes any skill or area where a person excels. For example, in professional settings, someone might say, "Negotiation is her strong suit," meaning that she is particularly skilled or effective at negotiating.