This is the 53rd most frequent Spanish word.
otros
"Others" or "the rest."
'Otros' is used here as an adjective modifying the noun 'libros' to specify those that are additional.
Los otros libros están en la mesa.
The other books are on the table.
'Otros' is serving as a noun here in its plural form, referring to additional unspecified paintings.
Prefiero este cuadro a otros que he visto.
I prefer this painting to others that I have seen.
'Otros' in this phrase functions as a noun preceded by the definite article 'los', referring to specific other people in context.