What does it mean, i.e. 'active picture (w/o VBI) height for D-10/IMX' ? And, what is D-10/IMX?
VBI stands for "vertical blanking interval", so the "height" variable includes only the true picture data, without any padding associated with vertical blanking.
D-10 and IMX are other names for the SMPTE 356M professional audio/video format. You can read a bit about it at https://en.wikipedia.org/wiki/SMPTE_356M, but you'll probably need to read the actual SMPTE document to find out why that comment is attached to the variable declaration. I know nothing about it, myself.