ID understanding golf course relations
When you visit http://www.openstreetmap.org and click the "Edit" button, you are brought into the map editor known as "iD". It is the default editor for OSM and tries to present the map in a reasonable way to the most users possible. Sometimes, there are concepts that are too complex to show in a clean, simple way. When drawing a simple golf course with a fairway that sits alone on the course and doesn't have any embedded sand traps, tees, putting greens, or water hazards, you simply draw a polygon and label it with a "Feature Type" of "Fairway". But when trying to show something like a fairway that surrounds a green with a fringe, it gets more complex and you have to say that everything within a polygon is a fairway, EXCEPT the part within the green.
It is quite common for people to see a golf fairway in iD and click on it expecting to see it properly tagged as a "Fairway" feature type, only to see it as a generic "Line" feature type instead. Thinking that this is wrong, they will then proceed to add a golf=fairway tag, not realizing that they are duplicating information that is already in a more complex representation of multiple objects, expressed as a "relation". With relations (in this case, a multipolygon relation), you can group multiple objects together to represent a single concept. That is, you can say that everything within the outer area is one thing, except for the area inside another object like a green that is a different thing.
You'll notice that when you select the outer ring fairway, that it shows that it is a member of a relation. (See the red arrow in the first screenshot.)
If you then click on that blue "Fairway" link in the left rail, it will expand to show you that the Fairway is defined as the "outer" border, and the "inner" cut-out is the putting green. It would be incorrect to add a `golf=fairway` tag to the outer boundary as that implies that everything inside that boundary is a fairway, including the putting green. The proper place to define the fairway tag is on the relation itself as seen in the second image:
