'Ain't no sunshine when she's gone It's not warm when she's away...' Great song. 'Ain't no sunshine' is an informal, non-standard way of saying 'There is no sunshine' or 'There isn't any sunshine.' This construction is common in popular songs. It's often used because it fits better with the music than standard grammar does. 'Ain't' can mean isn't, aren't, am not, has not or have not. You should recognise the form 'ain't' when you see it, but you shouldn't use it.

ain't: am not, is not, are not, have not, has not, do not, does not, did not. "I ain't seen it", "That just ain't so!", "You ain't seen nothin' yet!" Ain't it just colloquial?

"Ain't no sunshine" comes from a song sang by Bill Withers. It refers to sadness and loss at the end of a relationship. It is not typically used in conversation.

Thanks, Yevgeniya

it means "There is no sunshine" https://en.wikipedia.org/wiki/Ain%27t