When the Bob of a simple pendulum swings,the work done by tension in the string is zero how what is the meaning of swings.what is tension

Hello there!The term "Swing" simple means performing to and fro motion or oscillatory motion by the bob which is suspended by a string(massless).Tension is kind of pulling force which is being transmitted throughout the entire length of the wire by each ends of the wire. Here the pulling force is developed due to weight(vertically downward)and force exerted by point of suspension on wire.Now to calculate work done by tension force on the bob having mass m(say) we have to write W=FScosα where α is the angle between F(tension force on bob) and S(Displacement of bob).Here α is always 90° so cosα=0 hence W=0