The legal definition for personal data is any information relating to an identified or identifiable natural person. Which is the data subject. An identifiable person is one who can be identified directly or indirectly, in particular by reference to an identification number or to one or more factors specific to his physical, psychological, mental, economic, cultural, or social identity. What this means in short, is that personal data is any data which can be linked directly or indirectly to a natural person. There is also a sub-category of personal data called special categories of data or sensitive data
. This is data which can be used to discriminate against you, for example, health data, religion, trade union membership, etc.