what does the %2F refer to in the query string

Hi what does %2F  refer to in the query string. my Query looks like this:

HttpContext.Current.Request.Url.Query = " RootFolder=%2FLists%2FtskList2&ContentTypeId=0x010800009E7A9DBA6F3249BC69C8BECD548608008A8FCB4195F70F478AED6775A0D4F1D3&Source=http%3A%2F%2Frta%2FLists%2FtskList2%2FAllItems%2Easpx"

I know for a fact that tskList2 is the name of my curent list but what does %2F before the name of my list refer to

Thank you