A few times, I have seen partially-overlapping horizontal boards, creating a larger panel. For example, I've seen this done on the walls of some wooden houses. I would like to know if there is a joint between these boards, or they are just nailed / glued together. I didn't get the impression a tongue and groove were involved.
Without having a picture to go on, I'm going to take a guess as to what kind of joint you're describing.
This type of joint has two boards with matching rabbets on opposing faces and was commonly used in (you guessed it) ship hulls. In ship construction, these were normally pegged with trunnels. In furniture, they may or may not be glued, depending on how the ends are fixed to the piece.
Often times the "show" side of the joint will have a decorative bead, which helps to hide the joint. I couldn't find a suitable picture of this, but the one below (shaped in a solid piece, so not actually a shiplap) shows the effect.
These joints use a long spline to reinforce the butt joint and keep the boards aligned. Usually these are glued in place, so it may not be what you're seeing. Also, I doubt a house framer would go to the trouble of splining all the boards for a wall, but you never know.