"Cage-free" means that the hens laying "cage-free" eggs are, quite simply, not kept in cages. They are free to walk around the hen house, to perch on roosts, and to lay eggs in nests.
This is in great contrast to most laying hens, which are kept in cages so small that they can't fully open their wings, much less walk or move about. "Cage-free" eggs are also fairly widely available – and a solidly better choice than most commercial/industrial eggs – at mainstream grocery stores, unlike the less common pastured eggs.
That said, "cage-free" chickens are kept in hen houses, often in cramped conditions, and may or may not have access to the outdoors or pasture.