Delta wings are essentially giant triangles attached to a fuselage. This design is useful for low drag, structural strength, and internal fuel storage. Delta wings have excellent handling especially at lower speeds due to their increased lift. Delta wing aircraft were very common during the Cold War Era with designs like the Mig-21, Gripen, Dassult Mirage, and the Saab Draken. The Mig-21 uses a Tailed Delta design which increases stability. The Gripen uses a Canard Delta wing design helping with maneuverability. The  Dassult Mirage uses a Simple Delta without the tail that the Mig-21 has. The Saab Draken uses a Double Delta to improve lift and control at different speeds. Delta wings require extra runway space to take off and land due to their increased drag at lower speeds, and high angles of attack.

The featured image is the Gripen with canards (little front wings)

The Mig-21 with a tail

The Dassult Mirage with a Simple Delta

The Saab Draken with a Double Delta (two sided wings)