A pass, usually in the form of a laminated card or felt-like sticker, that allows the bearer access to the "backstage" area of an entertainment event (e.g., a concert). The area might not literally be behind the stage, but some other at the venue normally restricted to the other event attendees. An event may have different types of backstage passes for different levels of access; typically the "All Access" passes for a concert are of the laminated card variety, whereas the sticker type usually only allows the bearer access to limited areas at predetermined times.
Many music fans dream of getting a backstage pass so that they can meet their favorite bands at one of their concerts, but they should realize that 1) the bands their fan clubs don't always have the power to give out backstage passes; usually it's the venue or radio stations who get a hold of these, 2) like front-row tickets, backstage passes are mostly snatched up by those who already personally know somebody in the band, crew, or venue staff. And most importantly, 3) even having a backstage pass does not guarentee that you'll get to meet the band.