side letter的中文意思是“补充条款，补充协议”，指对原合同的补充或者变更，一般要明确约定，如果补充协议条款与原合同不一致或发生冲突时，应当以补充协议为准，但原合同明示不得变更的条款，补充协议中对该条款发生的变更则不发生法律效力。为了更好的理解该词，以下是其英文释义：A side letter or side agreement or side letter arrangement is an agreement that is not part of the underlying or primary contract or agreement, and which some or all parties to the contract use to reach agreement on issues the primary contract does not cover or that need clarification, or to amend the primary contract.

如:

Side Letters. Notwithstanding anything to the contrary contained herein or the provisions of any Subscription Agreement, including Section 14.3 hereof, it is hereby acknowledged and agreed that the General Partner, for itself or on behalf of the Partnership, and without the approval of any Limited Partner or of any other Person, may, to the extent that it does not conflict with the General Partner's obligations (including its fiduciary duties), enter into, perform, amend, modify, waive or terminate a side letter or similar agreement to or with a Limited Partner which has the effect of establishing rights under, or altering or supplementing the terms hereof or any Subscription Agreement, including terms relating to fees, Carried Interest and information and reporting rights;

补充协议。尽管本协议或任何《认购协议》(包括本协议第14.3条)有任何相反的规定，各方特此确认并同意，普通合伙人，为其自身或代表合伙企业，未经任何有限合伙人或任何其他人的批准，在不与普通合伙人的义务(包括其信义义务)冲突的情况下，可以与有限合伙人签订、履行、修改、修订、放弃或终止一份补充协议或类似协议，该补充协议或类似协议具有确立本协议或任何《认购协议》项下权利、修改或补充本协议或任何《认购协议》条款的效力，包括与费用、附带权益、信息和报告权有关的条款；