It is an order made by a local planning authority (in Norfolk this is done by the District Councils) which makes it an offence to cut down, top, lop, uproot, wilfully damage or wilfully destroy any tree protected without obtaining permission from the local authority. Its purpose is to protect trees which make a significant impact on their local surroundings. The order can cover anything from a single tree to woodlands, including hedgerow trees, but not hedges, bushes or shrubs. Further information is available from
https://www.gov.uk/guidance/tree-preservation-orders-and-trees-in-conservation-areas
Picture by Cornel Howells