From rave and club culture slang, a lammie is the laminated badge and necklace that signify one as a Very Important Person to the rest of the crowd. Generally they share design with the event's flyer or other promotional materials, having been cut down or photocopied from them. Often they will have lettering that says "Event Staff" or the like, and sometimes even more specific roles. Large (read: rich) promotion crews may have lammies printed separately in the same run with their fliers, giving them an altogether more professional appearance.
A lammie grants the wearer access to all staging areas, VIP rooms, parking lots in no-reentry events, and so forth. However, they're different from concert backstage passes in that they cannot be bought, but instead are given by the promoters to people who need them: DJs, security, sound and lighting crew, and the promoters themselves. Sometimes they are given to non-staff people, such as other promoters, DJ hoes, old-school scenesters, and sundry other Rave Royalty. This practice leads to confusion when a partier is looking for event staff to ask for help or timeslots, and finds somebody wearing a lammie who happens to be fucked up on drugs, clueless, or otherwise not helpful. Still, for anybody who gets one a lammie is a great souvenir, proof positive that they played a part in something that affected hundreds or thousands of lives over the course of a night.