[codeulike]

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

[disgruntledphd2]

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).