UVA stands for ultraviolet light A. There are three types of ultraviolet lights: A, B, and C. C does not reach the surface of the earth as it's absorbed by the ozone layer. UVA and UVB do reach the surface of the earth and are absorbed by our skin.
UVA does not cause redness of the skin so it's very hard to determine how much UVA light you are getting. It is absorbed by the DNA of our skin and can cause DNA damage. This DNA damage over time can lead to skin cancer. High levels of UVA during childhood is a risk factor for forming melanoma in the future.
Most over the counter sunscreens will not tell you how much UVA protection they offer. So it's important to read the ingredients and do some research to make sure that what you're putting on your skin provides adequate UVA coverage.