This is the 25th most frequent Lithuanian word.
tai
"Tai" in Lithuanian means "this," "that," or "it" depending on the context.
In this sentence, 'tai' is used as a demonstrative pronoun meaning 'this', specifying or indicating the object 'book'.
Tai yra knyga.
This is a book.
Here, 'tai' is used to refer to a concept, idea, or a general matter whose importance has changed, functioning as a pronoun.
Tai nebėra svarbu.
That is no longer important.
In this context, 'tai' serves as a pronoun referring to a hypothetical situation or condition proposed earlier in the statement.