"Zipper" and "Floater" are often used interchangeably. If you put in the blue search box you will find others' examples and usage.

Anyone that uses the terms interchangeably does not know what they mean.

A zipper verse is where the verse repeats through the song with minor changes.

Example: O Mother let's go down, down to the valley to pray.
Then: O Father let's go down, down to the valley to pray.
O Brother, let's go down, down to the valley to pray.
O Sister, etc.

A floating verse is a traditional verse that recurs in many different songs.

Example: This old hammer it killed John Henry
It didn't kill me, baby, couldn't kill me

That verse is in "Roll On Buddy," "Swannanoa Tunnel," "Spikedriver Blues," etc.