Most modern gas-powered appliances have their gas lit by an electric igniter, but older ones might still have a pilot light. A pilot light is a small flame that is fed by the gas line, and constantly burning to be available for lighting up the gas. Of course, this is a waste of natural gas, and it does also come with certain risks.
One possibility is that the pilot light goes out, leading to natural gas leaking out. While there usually is some type of fail-safe in place to prevent this from happening, it can still happen. If you ever have to deal with an extinguished pilot light, you should make sure that the area is well ventilated and that you don’t smell any gas before you try igniting it again.
If you do have appliances with a pilot flame, it might be worth considering investing in a modern appliance with electric ignition, removing the risk completely.