Within privacy-focused advertising, which data processing principle requires limiting data collection to what is strictly necessary for a defined purpose?

The data processing principle requiring the limitation of data collection to what is strictly necessary for a defined purpose is 'data minimization'. Data minimization, also known as 'purpose limitation' in some contexts, dictates that organizations should only collect personal data that is adequate, relevant, and limited to what is necessary in relation to the purposes for which they are processed. For instance, if an online retailer only needs a customer's email address to send a shipping confirmation, they should not collect their phone number, birthdate, or other information that is not essential for that specific purpose. This principle reduces the risk of data breaches and misuse, aligning with the core values of privacy-focused advertising by minimizing the amount of personal information handled.