Personal data is information relating to individuals who can be personally identified from that data (on its own or with other data held). Personal data can be held electronically or physically and includes names, addresses (including email addresses), dates of birth and online identifiers (eg IP addresses).
There is a further 'special category' of personal data which is subject to more restrictions. Special categories of personal data include information about racial or ethnic origin, sexual life and physical or mental health or condition.
For more information, read Data protection.