Hydro is a blanket term that, in general, refers to water or water-related activities.

It is sometimes used as a short form for hydroelectricity. In areas where hydroelectrical power is prevalent, such as Canada and Tasmania (Australia); it is essentially a synonym for 'electricity services' or 'mains'.

Many Canadian provincial electric-services companies have 'Hydro' in their name. They include:

• BC Hydro
• Hydro-Québec
• Hydro One (Ontario)
• Manitoba Hydro
• Newfoundland and Labrador Hydro

Municipal-level service companies in these provinces will also often feature 'Hydro' in their name.

Other provinces in Canada, such as Alberta and Saskatchewan do not have as much hydroelectric power and as such the term hydro is not a common synonym for electricity.

A Norwegian company is named Norsk Hydro, and there is a Tasmanian company named Hydro Tasmania.

Hydro also refers to a hotel in a spa town at which guests may 'take the waters'.

There is a town in the United States named Hydro, Oklahoma.

Hydro is a name for some types of Cannibis, sometimes referred to as 'dro'.