CBMP stands for "Contra Body Movement Position". When a teacher or a technical manual described a step as being in CBMP, it is an indication that you should place the moving foot either along or across the track of the standing foot.
When the step is described as being "forward in CBMP", you should place the foot along the track. When it is described as "forward and across in CBMP", you should place the foot across the track.
People will probably also mention to you that CBMP is a position of the body whereby one side of the body is in advance of the other (the side opposite the moving foot). This is true enough, but it's not something you need to concern yourself with. The position of the body is the natural result of having placed the foot correctly, and having turned the correct amount.
So don't concern yourself with the body position, as that tends to confuse, as well as create poor habits in your dancing. Just remember that when you see "CBMP", it's telling you explicitly to place the moving foot along or across the track of the standing foot. Everything else is implied.
Regards,
Jonathan Atkinson
