Any of several types of legal joinders whereby one or more parties unites with or joins other parties in a legal action or proceeding even though the party may not be a direct part of the action or proceeding. A third party has a supervisory interest in an action, but does not have a direct interest to the action. For example, a guardian is appointed by the courts to oversee the property interests of a minor. The minor agrees to sell a parcel property to another party and the guardian enters into a joinder agreement approving the sale of the property. Examples of legal joinders include collusive joinder, compulsory joinder, joinder in demurrer, joinder in issue, joinder in pleading, joinder of claims. joinder of defendants, joinder of parties, joinder of remedies, and permissive joinder.