EC stands for Bishop Williamson's "Eleison Comments" ...
https://stmarcelinitiative.com/eleison-comments/
It's a regular series of thoughts by His Excellency on various subjects ... typically once a week.
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I saw this question and was going to answer but found your post so there's no need now.
Good job.
We ought to keep in mind there are new readers here all the time and if we get too abbreviated they'll lose interest for bewilderment.
After all, "EC" isn't a standard English term so no one can "look it up."
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Oh, one more thing -- the ECs are also disseminated by e-mail, and if anyone like them, they can sign up for a free subscription.
(Of course, it would be polite to send in some contribution for the service)