An Economy 7 meter is a type of 2-rate meter. A 2-rate meter is an electricity meter which has 2 registers, recording what time of day you use your electricity (2-rate meters do not exist for gas). The most common 2-rate meter is called an Economy 7 but there are many others.
Unlike a 'traditional' meter, you may have 2 rows of numbers on your meter rather than just the 1 (if this has been recently installed it may only show one row on an electronic display but ). Each register will be labelled slightly differently to indicate which time period they relate to.
Scrolling through would then show the second rate,
These rates may be displayed as R1 & R2 or L & N.
If you do have a 2-rate meter, there are specific 2-rate tariffs available to you to take advantage of this functionality, where by you pay a different unit rate depending on when you use your electricity. You will generally pay more for electricity consumed during the daytime, and less in the night. Typically, people with immersion / storage heaters find that this option is best for them but this is not always the case!
Unfortunately unless you have a 2 rate installed we aren't able to offer a time of use tariff. If you would like to have a single rate meter exchanged for a 2 rate meter this would be chargeable.