In the UK (and a few other places) it’s “Mothering Sunday”, the day you honour the church where you were baptised, or your mother church.

https://en.wikipedia.org/wiki/Mothering_Sunday

Well that just seems like a completely different thing that share a few letters

I'm in the UK and I've never heard of that definition of it (being to do with churches), maybe thats a very ancient definiton

That's how the date is determined, it's the third Sunday of Lent, "mothering sunday". Hence why the date changes every year (as the dates of Lent move because Easter Sunday is the first Sunday after the first full moon after the Equinox).

Add a few more letters and you get my favorite day of the year