A Watch is a product issued by the NWS (National Weather Service) indication that a particular hazard is possible, i.e., conditions are more favorable than usual for its occurrence. A watch is a recommendation for planning, preparation, and increased awareness (i.e., to be alert for changing weather, listen for further information, and think about what to do if danger materializes).
A Warning is a product issued by the NWS (National Weather Service) indication weather hazard is either imminent or has been reported. A warning indicates the need to take action to protect life and property. The type of hazards is reflected in the type of warning (e.g., tornado warnings, blizzard warnings).
An advisory is a product issued by the NWS (National Weather Service) that highlights special weather conditions that are less serious than a warning. An advisory is for events that may cause significant inconvenience, and if caution is not exercised, it could lead to situations that may cause threatened life and/or property.