A supplement or sourcebook is a publication (other than a core rulebook) that contains information about one or more role-playing games (usually rules or setting information). Supplements are intended to enhance a group's experience of a game, either by giving them extra content for campaigns in an existing setting (e.g. character options, enemies, scenarios, or wholly new rules that can be used) or by giving guidance for using the existing game in wholly new ways (e.g. entirely new settings).
New rules from supplements are generally not considered to be house rules, although the fact that groups can choose to use them or not means that they are similar in practice.
- Splatbook, a supplement that focuses specifically on a single character type in a game