Sprint hotspot question re what 5gb means

MY wife just opted for the Sprint hotspot option and was told there was a 5gb a month limit.  I am confused about what that means.  Does that relate to downloads or does that mean that every time she surfs the internet thru the hotspot she is going to be accessed x amount of mbs or gbs?

In other words, is there a limit to how much internet surfing you can do before being charged or does that limit just relate to downloading files i.e. movies; videos; music, etc.

Thanks