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 the electronic display at a time). 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 meter 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.