There is material online about histology yield, often compared with cytology yield, in relation to different types and sizes of biopsy needles. It seems clear that the point at issue is how much useful tissue is extracted in the biopsy for one type of analysis versus another, bearing in mind that cytology is to do with loose cells whereas histology is to do with miscroscopic anatomy of tissues, so presumably a different kind of material is required depending on which it is for.

Here, for example, is an article entitled "Prospective pilot evaluation of a new needle prototype for endoscopic ultrasonography-guided fine-needle aspiration: comparison of cytology and histology yield". The abstract makes it clear that "yield" means material extracted with a needle in a biopsy:

"In each patient we aimed to make two needle passes, and if the material acquired appeared insufficient macroscopically (no in-room cytopathology was available), further passes were done. The material was sent for cytological and histological assessment."
http://www.ncbi.nlm.nih.gov/pubmed/18334879

But the most useful document I've found is this one, on types of needles for this purpose:

"In recent studies, Kenneth Chang, MD, Executive Director, H. H. Chao Comprehensive Digestive Disease Center (University of California-Irvine), found that a new 25 gage biopsy needle developed by Cook Medical combined the attributes of both FNA and FNB, and delivered a single-pass diagnosis of 88% in suspected tumors of the pancreas when pathologists examined both the histological and cytological yield obtained.
“We haven’t done a head-to-head comparison yet,” says Dr. Chang, “but I think we’d be able to say that this 25 gage needle is as good if not better than the standard 25 when comparing cytology yields [...]
“I was already familiar with the 19 and 22 gage ProCore needles,” Dr. Chang continues. “But eventually we asked a simple question: ‘What would happen if you made a 25 gage EUS needle in the same configuration?’ The initial thought was, of course, you’re going to have a worse yield. Because you’re looking at a core needle that is smaller; therefore, the yield should decrease. But, pushing that assumption aside, we knew that if we didn’t try we would never know for sure. So, based on initial discussions, Cook Medical decided to manufacture a limited number of 25 gage needles. And, so far, we feel that it outperforms the 19 gage and the 22 gage for tissue acquisition."
https://www.cookmedical.com/documents/42434/0/The_Channel-is...

You need to remember that the higher the number, the smaller (thinner) the needle.

So yield, clearly, means tissue acquisition, and histology yield is acquisition of suitable tissue for histology as opposed to cytology. The "market shift to histology yield" may means that the market in medical equipment is placing greater emphasis on needles with a good histology yield as opposed to cytology yield.