I think the author is referring to a subset of discrete choice experiments in which the actual products on the marketplace are more closely represented, rather than in a traditional conjoint experiment wherein the attributes are left to vary freely to create all sorts of product concepts that may or may not necessarily be represented in the marketplace.
As an example, imagine a marketplace in which the products could be broken down into six different attributes (with the sixth attribute being price), each with 4 levels. There are 4^5 = 1024 product concepts (aside from price differences) that could be presented to respondents.
However, with a discrete choice experiment that aimed to more closely align with actual product definitions on the marketplace, maybe the actual products as existing in the marketplace are defined as fixed alternatives on the first 4 attributes (say, 8 possible fixed product alternatives, each described using just one level of each of the first 4 attributes), the 5th attribute perhaps is allowed to vary across its 4 levels, and the 6th attribute (price) also varies (perhaps in a conditional pricing design, so that the ranges of prices are customized for each of the 8 possible fixed alternatives).
With such a design as above, respondents tend to be seeing products in the CBC (discrete choice) survey that are more realistic (and recognizable) as those that currently exist in the marketplace. This has the benefit of producing a more realistic CBC interview, where the preference captured for the existing products in the marketplace are potentially more accurate. However, it has the drawback that if the researcher wants to examine what other combinations (other than the 8 fixed product alternatives) could be constructed using the first four attributes, it would be impossible to examine that given the data.
There are hybrids of the same idea above. For example, maybe four of the product alternatives are fixed across all their attributes; two of the product alternatives are allowed to vary freely on just two of the attributes; and another two are allowed to vary across all attributes.
All the designs I've described above may be accomplished with Sawtooth Software's CBC system with its Advanced Design Module.