Salt aka NaCL, Sodium Choride, is 40% sodium and 60% cloride. This is a trace mineral that is essential to our bodies. Apparently we need about 200-500mg per day for daily body function. However, it is common to oversalt food, and processed foods are heavily oversalted (to add taste to tasteless products). Excess salt increases blood pressure and the risk of strokes, heart attacks, and kidney disease. Children especially are susceptible to this, and the CDC says 90% of children consume too much salt.
An example is Kraft Macaroni and Cheese, which has 560mg of salt per serving, which it claims is 24% of the 2,400mg daily value. The CDC suggests less than 1,500mg of salt per day for many groups, and as we see above, only 500mg is actually needed. This is a highly processed and oversalted food that should be avoided.