What does shiro mean in Japanese?

It is the color white. Improved Answer: That's close, but no. Shiroi means White. Shiro means Fourth Born Son.

Improved Answer: ^ Also close, but shiro and shiroi both mean white. Shiro is used as a noun while shiroi is used as an adjective.

For example:

Kono kappu ha shiro desu = This cup is white.

Kore ha shiroi kappu desu = This is a white cup.