What is does a number 4 buoy mean?

A number 4 buoy typically indicates a lateral marker used in maritime navigation, signifying the left side of a channel when entering from the sea. It is part of the IALA (International Association of Lighthouse Authorities) buoyage system, specifically following the "IALA A" system, which is used in most parts of the world. The buoy is usually colored red or has a red band and may also feature a specific shape, such as a can or cylinder, to help mariners identify it easily.