The FDA is stepping in to regulate how SPF can label itself. Gone are the days that something can label itself a sunblock, since it is not really possible and products are no longer allowed to claim to be waterproof or sweatproof. Sunscreens will be able to label themselves "broad spectrum" (meaning they protect against both UVA and UVB rays) if they protect against all forms of sun-related skin damage. Burns are mostly caused by UVB rays; while UVA can also cause sunburn, they also can cause skin cancer and premature aging. Ick!
Bottles will also have a labeled time frame for which you should expect to be protected before reapplication is necessary. If a sunscreen claims to protect for longer than 2 hours, they will need to submit data to support their claim and get approval from the FDA, the same goes for products stating immediate protection upon application.
In the next year this new labeling will be put into effect, making it easier for consumers to choose the right sun protection for themselves. Inform yourself here, and don't forget to always wear sunscreen!