If a place or a vehicle is fogbound, thick fog has stopped people travelling or working as usual. Planes stay on the ground, ships wait in the harbour, a town can feel shut in. You will hear it in weather reports and travel news. It is a fairly newspaper-ish word; in speech people often just say stuck because of the fog, or the airport is closed due to fog. The -bound here means held in place by something, not bound as in a book, and not bound for a place. Though actually, English builds the same pattern with other weather: snowbound is the twin you are most likely to meet.