This is the 6171st most frequent Russian word.
твое
"Твое" means "your" (neuter singular).
The word 'твое' is used here as a singular, neuter possessive pronoun indicating ownership of the apple by the addressed person.
Это твое яблоко.
This is your apple.
In this sentence, 'твое' modifies 'мнение', which is a neuter noun, to indicate that the opinion belongs to the person being addressed.
Твое мнение важно для нас.
Your opinion is important to us.
Here, 'твое' precedes 'письмо', a neuter noun, to denote that the letter is possessed by the listener addressed.