Why does "borad-spectrum" mean?

     Broad-spectrum sunscreens provide protection from both UVA and UVB rays. When used as directed, these sunscreens will not only protect against sunburn, but also reduce the risk of skin cancer and premature skin aging. Sunscreen alone cannot protect the skin from 100% of the sun’s harmful rays; therefore, it is recommended to seek shade when outdoors, especially between 10:00 AM and 4:00 PM, and wear a wide-brimmed hat, long sleeves, and sunglasses when exposed to direct sunlight.