이다 is the Korean verb meaning "to be". It is used to link a subject with a predicate (also called a copula in Linguistics). Based on setting and speech register, you will it appear in numerous forms but the three most common are listed below:
이다 (dictionary form, very casual)
이에요 (generically formal, polite)
입니다 (humble form)
You will use 이에요for the vast majority of your communication in Korean.
Survival Korean
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Survival Korean