Pugger is a noun derived from the the acronym PUG, for Pick Up Group. This refers to a person (in an MMOG) who bands with you in the interest of achieving a shared objective. A pugger has a dubious amount of skill and therefore may be of little use.
Among circles in online communities, specifically Multi-User-Online-Games(MMOs) such as World of Warcraft, There are two types of people you may encounter: People that belong to your extended social network, and people you don't know. A pugger takes the form of the latter: a passerby.