If something's adrift, it's floating, not tied down or anchored. A raft that's adrift on a river will float downstream.
If a ship goes adrift, it meanders off course, simply traveling with the water rather than on a charted course. Likewise, if you feel your life has gone figuratively adrift, you may have lost track of your plans and feel like you're wandering without a purpose. The word adrift comes from the sense of drift that means "a slow movement from one place to another," from an Old Norse root word.