Making an “agreement”: is a quasi conversational contract to clarify potentially uncertain boundaries in the conversation. Sometimes in the normal interchange of social relations the agreement can be tacit--something both parties knows exists while in others, especially when you sense reluctance, raising the issue may serve to make both (or all) of you feel more comfortable.
In the latter case an informal agreement about the boundaries and tone of the conversation allows both parties to speak their minds and verbalize their critical analysis of each other’s position on various topics. This agreement can range over a span of issues including topics like politics, religion, family, and other personal things. To repeat, the agreement is typically a verbal agreement (almost never written) to which both parties give some form of assent. Working out how to do this tactfully and with sensitivity can help both parties a degree of comfort and freedom to express their opinions that not every conversation enjoys.