Grammar problem from a dictionary

Hello! I found this explanation of “prayer” in a Cambridge dictionary:

“A prayer is the words that someone says or thinks when they are praying”

I don’t understand why “they are” is used for “someone”. Isn’t “someone” singular, because it is followed by “says” and “thinks” ???

Please explain this to me!

Grammatically you are right, and if you are taking a language proficiency test, you should correct this to he or she is.

However, in spoken English, they/their/them have been the pronouns for singular persons of unknown gender for centuries, and they are more and more widely accepted in most situations these days.