A chord is just multiple notes played at the same time, usually because they sound nice together. A chord progression is just a series of different chords used in a particular order to give structure to a song. You can see [a hilarious video](https://youtu.be/5pidokakU4I) of lots of songs that use the same chord progression on YouTube.
I haven’t read the opinion in the case, but generally, you can’t copyright a chord progression because it’s too basic. Sheeran’s song is an R&B ballad. That means it *has to* have certain qualities to its tonality and rhythm that make it sound like an R&B ballad. Adam Neely [sums it up nicely](https://www.youtube.com/watch?v=Tpi4d3YM79Q). You can’t own chords.
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