Mondegreen

Also known as misheard lyrics.

When a columnist named Sylvia Wright was a child, 

she mis-heard a Scottish ballad

"They have slain the Earl of Murray

And laid him on the green." 

as

"They have slain the Earl of Murray

And the Lady Mondegreen."

So Ms Wright named accidents of mis-hearing like this Mondegreens.

Several websites are dedicated to this topic.

While rap and hiphop lyrics seem to be

most easily misheard, when I was a child we sang a hymn: 

"You, who unto Jesus for refuge have fled..."

and I still mentally hear "yoo-hoo unto Jesus"

and this one:

"O refresh us, travelling through this wilderness"

I mis-heard as "O refreshments"