Definition
A personal data processing activity is defined simply as any operation relating to personal data.
It may be a single operation or several operations forming a set with the same purpose.
The simple list of the operations performed on data is not enough to define a a data processing activity. Article 4 of the GDPR gives a non-exhaustive list: collection, recording, organisation, structuring, storage, adaptation or alteration, retrieval, consultation, use, disclosure by transmission, dissemination or otherwise making available, alignment or combination, restriction, erasure or destruction.
In practice, it is a use of personal data.
This use may be automated or not. In other words, the use may be the result of a computer process operated by a computer (for example, saving a computer file on a hard disk) but may also be a paper process (for example, accounting or legal files stored in a cupboard) as long as the data in paper format is structured.
The aim is obviously to limit the application of the rules to IT and to cover archives and printed paper files.
Writing contact details on a corner of a table is unlikely to constitute processing if they remain in a portfolio and the writing is only used to transmit information.
It would be different if the details were then entered into a contact management software programme.
Processing can be more or less complex.
Sometimes it will involve a single use of data, for example, the sending of commercial canvassing by email and other times it will involve a complex set of operations involving several data for several uses. Processing carried out by government departments is a good example. The decrees authorising such processing very often cover a large number of operations.