I don't know, but I'd think it could be:

sink, toilet, shower, tub

or

sink, toilet, shower/tub, bidet

As long as there are 4 "fixtures" in the room, it' 4 pieces.

talley has got it right, 4 fixtures..maybe a urinal? Can't believe that this is becoming a trend

May be something else that is regional..
Here a 4 piece bath is considered tub, shower (may or may not be separate from bath), sink and toilet.

Separate tub and shower.

Here it is also sink, toilet, shower, and tub. The tub/shower are typically combined though and it still counts as 4 pieces.

Technically, the number refers to the plumbing runs. Therefore a 4 piece bath could have many options; sink, sink, toilet, tub or tub, shower, toilet, sink or toilet, bidet, sink , shower. Any combination qualifies, so you need to ask what the combination is to see if it suits your needs.

This post was 5.5 yrs old. Did you resurrect it, or did GW before you commented? I'm curious to know if it was a glitch.

kirkhall, it was probably a spammer who revived the thread. The spammers seem to be out in full force at GW the past few days.

GW deletes the spam post, but the thread stays in the new, revived position in the forum. Then people add new posts, because lots of us don't check the posting date carefully.

lol