Is thon in french masculine or feminine?

'ton' is generally used for masculine thing or nouns, and 'ta' for feminine nouns.

ton père (your father)
ton ami (masc. - your friend [a male one])
ta mère (your mother)

But 'ton' can also be used for liaison purposes, when the following noun begins with a vowel sound.
ton amie (fem. , exception to the general rule)