When you buy a townhouse, it comes with a community, and that community has amenities. Most townhouse developments have a gym, a pool, a laundry room, tennis courts and even a recreation room that owners can sign up to use for parties.
Say your townhouse community doesn't have one of these things, like tennis courts, and you know in your heart that you are the next Roger Federer or Serena Williams. (You're not, but let's go with the example.) In many townhouse communities, owners can pool their money to get these facilities added, as long as there's room to add such things on the property.
Officially, as a townhouse owner, you own a percentage of each of the common facilities. So if there are 50 units in your development, you own 2 percent of the laundry room. If you choose to think of one of the sofa cushions in the rec room as your 2 percent, go ahead, but be aware that almost no one else in the development will agree with you.