A safeclaim is a role name provided by the moderator at the beginning of the game that is guaranteed to be safe to claim; that is, it will not be counterclaimed by a Town role. These are usually only seen in themed games, and usually do not extend to telling the player what role abilities to claim.
Moderators started to give these out so as to make massclaim less of a breaking strategy. It is not nearly as easy to pick out who the scum are when everyone in the game is claiming a role that is pro-Town in flavor.
There is a science to deciding what kinds of flavor names should become falseclaims - for instance, only giving the scum minor characters for their falseclaims will not help them much. The modding guides on this wiki go into this in greater detail.