If you don't make any claims on your policy (i.e you don't have any accidents or damage to your car), you will earn a 'no-claims bonus,' sometimes also known as a 'no-claims discount.' You can build this up each year and transfer it between insurance providers.
A no-claims bonus means you get a discount on future policies, which is usually worked out as a percent of the total.
The amount of discount you get will vary between insurers. The maximum you can enter is twenty years, however not all providers will offer a discount on this length. In this instance, your quote will include the highest no claims discount that the provider offers.