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. Station Officers in New Zealand wear red helmets with one blue stripe (prior to November 2013, they were yellow with one blue stripe).
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 This change has meant the traditional ranks have gone and been replaced by a role based name for the duty performed.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.