This is the 1st most frequent Estonian word.
on
The Estonian word "on" means "is" or "has" in English, depending on the context.
In this sentence, the word 'on' serves as the third-person singular present tense form of the verb 'olema', which translates to 'is' in English. It's used here to equate or identify 'See' (This) with 'raamat' (a book).
See on raamat.
This is a book.
In this example, 'on' conveys the state of being in the sentence, connecting 'Ta' (They/He/She) with 'õpetaja' (teacher).
Ta on õpetaja.
They are a teacher.
Here, 'on' is functioning as the verb 'is' in third-person indicating the location of 'raamat' (book) concerning 'laual' (on the table).