Otherwise it is a mess. There is the letter soup (WSXGA+, WQUXGA,... ), the lines (1080p, 720i,... a throwback to analog CRTs), the HD (Full HD, HD ready, ultra HD,...), the K (4K, 8K,...)...
Is it that hard to use 2 numbers?
You had VGA (640x480) for example.
But I do agree we should have called it 2160p not 4k, but marketing guys are like that.
Also, annoyingly enough, QHD itself can stand for "Quad HD" or "Quarter HD", the old smartphone standard of 960x540, which admittedly has pretty much entirely fallen out of use
If anything 2K and 4K and 1440p are the more marketing terms because their ambiguity allows companies to apply them to products in a misleading way to market their product as something better than it is.
"c" could mean Colour. Bob uses a c2160p monitor!