A meter or metre is:

• a unit of measurement: see metre
• a device for measuring (such as parking, water etc.): see measuring instrument, meter (electronics)
• a parking meter, water meter , electric meter , postage meter
• a person who reads these is a meter maid
• a concept in poetry: see meter (poetry)
• a related concept in music: metre (music)
• a funk band: see the Meters

In the USA "meter" is used for all of the above. In the UK and other Commonwealth countries, "metre" is the unit of length and the poetical and musical concepts, and "meter" is used for measuring devices. See also the page about American and British English differences.