"is used to be" is not a common combination of words. My guess is that you are just thinking of two different uses of "used to": In the first kind of usage, "used" has its normal meaning as the past tense or past participle of the verb "use", and "to" means "in order to". For example, "This is the pen (that) I used to write my essay" means that you wrote the essay using that pen.
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