These are designated areas of historic and architectural interest in which there are legal restrictions on what changes can be made to buildings, greenery and street furniture in order to preserve the unique character of the place.
Impact on planning decisions
Permitted development rights are more limited and you will need planning permission for works that are restricted. Works done in a conservation area will usually need to be particularly sensitive to its historic environment and in keeping with the area's character.
Responsible organisations and guidance
Local planning authorities are usually responsible for designating conservation areas. Although Historic England and the Secretary of State can also designate them. Historic England gives more information on how this works.