ODP / OAP or ODAP

Optional Defense Pacts (often referred to as ODP's) are a type of interalliance treaty wherein the signatory alliances may optionally defend each other if attacked, though such action is not required as it would be for a MDP. In practice, ODP's often function as ToA's. One variation of an ODP is the Optional Defense and Aggression Pact (oDAP/ODoAP/ODAP), wherein an alliance may both optionally defend another if attacked and optionally participate in aggressive actions with other signatories.
They are one step above ToA's and one step below MDP's