The first highlight is that Google is using the relatedness of terms:
For example, if you search for [principles of physics], our algorithms understand that "angular momentum," "special relativity," "big bang" and "quantum mechanics" are related terms that could help you find what you need.
SearchEngineLand's has a post on the topic, which provides very high-level overview of how it works. The creator, Ori Allon, created technology called Orion that was acquired by Google in 2006. However, I can't seem to find any publications describing the details, which is a bit unusual for academic work.
In other news, Google is also adjusting its snippets to be sensitive to query length: longer queries may return longer keyword-in-context snippets.
When you enter a longer query, with more than three words, regular-length snippets may not give you enough information and context. In these situations, we now increase the number of lines in the snippet to provide more information and show more of the words you typed in the context of the pageThese are small changes, but still interesting.