The ability to understand your partner’s perspective. Unfortunately English gives several different meanings for empathy. Affective empathy is related to sympathy, compassion, and feeling your partner’s feelings. I use empathy to refer to cognitive empathy - that is understanding their thinking and thoughts on a matter. There is no need to agree with them to have accurate cognitive empathy. You just need to be able to explain why they think the way they do on a subject.
Empathy is a key element in meeting your parter’s needs. It is hard to meet a need that you are only guessing at. Usually if you can understand their needs, and you know your own, creative ways can be found to meet most of both.
Empathy is related to theory of mind (the capacity to understand that other’s thoughts, beliefs, desires, might be different to our own).
https://en.wikipedia.org/wiki/Empathy#Classification
keywords - walk to understanding, accepting differences, assumptions