This is the 584th most frequent Italian word.
amico
Friend.
Here, 'amico' is used as a singular noun meaning 'friend', referring to a single male friend.
Ho un amico che vive in Italia.
I have a friend who lives in Italy.
In this sentence, 'migliore amico' means 'best friend', emphasizing a male friend who is close and special.
Il mio migliore amico mi ha aiutato con il trasloco.
My best friend helped me with the move.
Here, 'amici' is the plural form of 'amico', referring to multiple friends collectively of unspecified gender.