For what it means: from a legal viewpoint, a lot; from the viewpoint of how you use
DVC, nothing.
A unit is usually a group of rooms. Each unit has its own use year month. When you buy you receive a percentage ownership interest in a particular unit in the resort along with percentage ownership interest in the common elements of the resort (pools, hallways, lobbies, front area, all the treees, etc.). That is actually what you own from a legal viewpoint. You don't own points per se because, and this may amaze many, they have absolutely no value from a legal standpoint. It is so deemed in your documents.
However, points are designated as "symbols" that represent your valuable ownership interest in the resort which is the real estate interest you have in that unit. So the process is to use points to reserve "vacation homes," which is another term in the documents. "Vacation home" is what everyone thinks of when they think of a room, a studio, a 1BR, etc. You never have to stay in your unit and it is mere happenstance that you ever do; you can stay in any of the rooms (vacation homes) in the resort.
In other words, for using DVC, points and rooms are what you will always be concerned with. But what you actually own is a small percentage of a unit.