Safe Zones are the blue circles around most stations (Recycle Stations, Upgrade Stations, Warp Gates, Weapon Factories, and Hangars) in space. Most Safe Zones are stationary, but some of them move in orbits. As long as you are in a Safe Zone, nothing can damage you. Your weapons are disabled when you are inside a Safe Zone.
Safe Zones are also the points where you respawn after someone or something kills you. You always respawn at the last Safe Zone that you visited. When you close the browser window or get disconnected in any other way, your ship will be back at the last Safe Zone you visited.