Unattached things are not connected or fastened. People can also be unattached, which usually means they don't have a long-term sweetheart.
If you pull apart two pieces of Velcro, they're unattached. If your tent comes unattached, or disconnected, from its pole, it may collapse. If you're a freelance reporter, you work unattached to a particular paper or magazine. When we say a person is unattached we mean they are not in a committed relationship. In the animal world, unattached means "free to swim around."