Australia and New Zealand
In Australia and New Zealand a Station Officer is either the single officer on a watch in a single-appliance station, with three firefighters reporting to them, or one of several officers under a Senior Station Officer at a station with multiple appliances. In New Zealand the rank badge is a single impeller. In Australia the rank badge is two impellers.
In the United Kingdom, a Station Officer used to command a station or was responsible for several watches commanded by Sub-Officers (although they may have commanded a watch on a very large station). The rank badge was two impellers, they also had a white helmet with a half inch black band around it.
More recently (2006/2007), the UK FRS has changed from a rank based system to a role based system. This change has meant the traditional ranks have gone and been replaced by a role based name for the duty performed. The two impeller marking now represents a Watch Manager. A Watch Commander (also referred to as a Watch Manager) is an officer who lead groups of firefighters and sometime in charge of a station. A Station Commander or Station Manager is an officer in charge of 1 or more fire stations. 
Republic of Ireland
The Fire Services in the Republic of Ireland also use the rank of station officer. In the full-time brigades of the five cities, they fulfil the role of watch manager, whereas in the retained county brigades, they fulfil the role of station commander. Rank markings are 2 impellers, and on the fireground a white helmet with black comb and 1 black stripe.
In the United States, "Station Officer" is often a general term and has several meanings. It usually refers to the senior officer at the station, often a captain or a lieutenant. A Station Commander is an officer in charge of 1 or more fire stations often referred to as a District Chief in North America. If a Battalion or District Chief works out of a station, a Captain or Lieutenant is still usually the officer in charge of the day-to-day operations of the station. In some cases the term "station officer" is used to differentiate between an officer who works in the field and a staff officer.
In many areas there is a Captain on every shift (watch) at a station. This means that each shift has its own station officer. In some departments there is a designated officer who is in overall charge of the station.