There are a number of db scales. This is 80db SPL which is sound pressure, it refers to the volume of the sound coming out of your speakers.
Recording levels in a digital realm are measured as db FS. The FS is for Full Scale. 0db is as high as you can go.
Recording levels on analog equipment are measured as dbVU (volume units) On this scale, 0db is the level that will give you a line level signal. You can exceed 0db by a certain amount before distortion. What ever that certain amount is is called headroom.
There are also dbu and dbv which are used in measuring voltage. There is also something called a DB that I can't remember what it is for. (it isn't used very much)