Blobber is a slang term that is used loosely to refer to first-person party-based RPGs in which the player controlled party is not represented as a distinct visual entity in the game world. As such, the game must stay in first-person view at all times within the game world (so that the camera can never be pointed at the party). Functionally, this means that the player's party always stays together and moves and acts as a single unit. No member of the party can be separated spacially from the rest, so, for instance, one party member cannot be commanded to walk down a hallway while the rest of the party waits behind. Thus, the party only has physical presence within the game world in the forms of walking around (i.e. having legs), swinging weapons or casting spells (i.e. having arms), and staying glued together as a solitary mass (i.e. being a blob). This artifice came to be called "a blob with arms and legs" and games that used it were in turn called "blobbers".
Blobbers originated as much out of technological limitation as intentional design in the early 1980s. Computers of that era were very limited in how much they could visually represent on screen, so maintaining a first-person view at all times was used to avoid the need to draw and animate the player's party characters on screen. As a result, scarce computer resources and screen real estate could be dedicated to showing just NPCs and the environment of the game world (which was still far from fully achievable). The necessity of using first-person view in blobbers was also desireable for closely imitating the experience of playing Dungeons & Dragons in which a Dungeon Master tells players about their perception of the game world in second person and the player issues their actions in first person. In early computer RPGs such as blobbers, D&D was nearly always the overwhelmingly dominant source of inspiration, so any method of better simulating the D&D experience was seen as a prime objective.