A links golf course, sometimes referred to as a seaside links, is the oldest style of golf course, first developed in Scotland. The word comes from the Scots language and refers to an area of coastal sand dunes, and sometimes to open parkland.
Many links – though not all – are located in coastal areas, on sandy soil, often amid dunes, with few water hazards and few if any trees. This reflects both the nature of the scenery where the sport happened to originate, and the fact that only limited resources were available to golf course architects at the time, and any earth moving had to be done by hand, so it was kept to a minimum.
So what made the 9-hole course “links-style”? First, there were no trees throughout the course. Second, there was only one water hazard, which was part of only one hole. Third, there were sand traps on eight of the holes. Finally, it was fairly flat. The combination of the flat land and no trees made the course windy, which is also an important factor. Hence, the “links-style” course.
The Wikipedia definition continues:
The challenges of links golf fall into two categories. Firstly the nature of the courses themselves, which tend to be characterised by uneven fairways, thick rough and small deep bunkers known as “pot bunkers”. Secondly, due to their coastal location many links courses are frequently windy. This affects the style of play required, favouring players who are able to play low accurate shots.
One word that keeps popping up in the definition is “coastal”:
Links courses tend to be on, or at least very near to, a coast, and the term is typically associated with coastal courses. However, links conditions can be duplicated on suitable ground, even hundreds of miles or kilometres inland. One especially notable example of an inland links-style course is Sand Hills Golf Club, a much-acclaimed early-2000s layout in the Sand Hills of Nebraska.
Links courses remain most common in Ireland and also in Great Britain, especially in Scotland. There are well known links courses in other countries, including in North America: Pebble Beach Golf Links in California (on the Pacific Ocean) and Whistling Straits in Wisconsin (on Lake Michigan) in the U.S.; and, in Canada, Harmon Seaside Links (in Stephenville, Newfoundland and Labrador).
The rest of the Wikipedia entry lists some famous links golf courses.