The Retainer
The word "retainer" refers both to the agreement between the lawyer and the client, and the "money retainer" held by the lawyer in his trust account to pay for legal services.
The existence and the amount of the "money retainer" held in trust is dependent on the complexity of the case and generally represents the maximum lawyer fees and disbursements expected to be billed to the client within one billing cycle (typically once per quarter).
For each client the agreement would be amended to match their individual circumstances and the type of legal matter being dealt with.