What's the difference between survivorship rules and merge agreement rules?

Survivorship rules are a collection of business rules defined for the creation of the best version record intelligently, especially from multiple source systems, by specifying criteria for selecting record and attributes to be retained during merge or link operations.

A merge agreement rule is a collection of patterns and conditions that are defined to determine whether a merge request should be vetoed by the application or not. Merge requests that violate these rules are either rejected or end in error.