A search term is composed of multiple keywords. Keyword proximity indicates how far apart the individual keywords are within the search term.
For instance, if a website includes the keywords from the search term “dentist Boston implant” in a heading like “Your professional dentist in Boston; dental practice for minimally invasive implants,” the proximity between “dentist” and “Boston” is one word, while between “Boston” and “implant,” it spans five words. The closer the keywords are to each other, the more relevant the search term becomes from a search engine perspective.