Murderhobo (or murder hobo, etc.) is a term used (originally pejoratively, but occasionally affectionately) for the player characters in RPGs, both in video games and tabletop games. The term arises due to the fact that most adventuring characters and parties are technically homeless vagrants, generally living on the road and sometimes in temporary accommodation, and the default solution to problems faced by the typical adventurer boils down to killing things until the problem is solved or treasure is acquired. In many games (especially older pure hack and slash-types of the type that Gary Gygax despised) killing things and taking their stuff is simply the order of the day, all morally acceptable and proper, either because that's all the players are interested in doing or all the GM can come up with. In more nuanced settings, "Murderhobo(s)" is used especially to refer to characters (or entire parties) of looser morals who tend to regard massive collateral damage as an inevitable and unremarkable consequence of their actions, or who are quite happy to slaughter otherwise friendly NPCs at slight provocation or the prospect of financial gain (basically, munchkins).
Although it is a fantasy standard that adventuring parties are welcomed into towns and villages and hailed as saviours, there is a small trend for this to be inverted in some games and stories (usually for comedy's sake) and have the protagonists be treated as the homeless serial killers they actually are, either by having them rejected from civilised society or by having the NPCs/minor characters respond with pants-shitting fear whenever the heroes present themselves. Murderhobos left to their own devices are bad news for the region they occupy, so they are often dealt with by giving them quests that take them to dangerous places in distant locations, where they can kill some other monsters (or at least some foreigners).