In Roman Catholicism, a Patron saint has special affinity for a trade or group. St Florian is the patron saint of firefighters, and Saint Christopher is the patron saint of travellers, for example. Eastern Orthodoxy generally doesn't associate saints with occupations and activities, or does so to a much lesser degree.
Patron saints can also be associated with geographical areas: Joseph the Betrothed is the patron saint of Belgium, and Saint Patrick is patron saint of Ireland, for example.
Saints associated with occupations and activities
Saints associated with countries, nations and/or regions
Saints associated with protection from ailments or illness
See also list of saints