As SD1 says, it looks like tyre carcase,cords damage causing a bulge in that area of tread, especially when you look at the sipes which should wear more or less equally.
It you compare the depth of the top one, with the others down the tyre they all get shallower.
Jack the wheel slightly clear of the ground, spin it slowly and see if you can see or feel a bulge in the tyre, BUT DON'T GET YOUR FINGERS UNDER THE TYRE.
Either way with that type and extent of abnormal tread wear it needs replacing as soon as .
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