An exact match domain or EMD is a domain name that matches precisely a targeted search engine query to obtain high rank in SERPs for this query.
Exact match domains are intensively used in SEO because search engines give high importance to domain names as an indication of a website topic. Thus, for many (niche) queries, a relatively large proportion of first page results are occupied by EMD.
An example of presence of exact match domains in SERPs:
Google has announced in 2012 that it wanted to reduce the amount of low quality exact match domains in search results. According to different barometers aimed at measuring EMD presence in Google SERPs, the announcement has been followed up as some exact match domains have gone down in SERPs.
However, it seems that EMD which have also other SEO and content qualities than their domain names have still an advantage in SERPs. Low quality EMD like MFA websites seem to be especially targeted by the algorithm change.
Exact match domains are used for doorway domains or main websites. They are especially useful for specialized activities for which a good part of search engine traffic comes from one type of query.
Some actors used EMD to gain free traffic in a domain of activity in which they have no offers and then monetize the traffic through AdSense, affiliates program or lead reselling.
Another example of EMD impact: