Definition 1 of 2
Close the door, begin when you undress and continue singing all through the bath until you are dressed again.
The tricky times are when you want to brush your teeth during the bath and so, you can't sing audibly. Then you lean on the door or keep a bucket or a foot against the door. Or run the tap on a bottom upped bucket, or do tap dancing.
On a day when you want to design an accidental entry of an interesting person, you just go dead silent.
Definition 2 of 2
Bride to be: Umm..will bathroom singing do?