Under GDPR Article 4(1) ‘personal data’ means any information relating to an identified or identifiable natural person (‘data subject’); an identifiable natural person is one who can be identified, directly or indirectly, in particular by reference to an identifier such as a name, an identification number, location data, an online identifier or to one or more factors specific to the physical, physiological, genetic, mental, economic, cultural or social identity of that natural person.
Here's a good resource that explains in detail from the European Commission.
a name and surname;
a home address;
an email address such as name.surname@company.com;
an identification card number;
location data (for example the location data function on a mobile phone)\*;
an Internet Protocol (IP) address;
a cookie ID\* Note that in some cases, there is specific sectoral legislation regulating for instance the use of location data or the use of cookies – the ePrivacy Directive;
the advertising identifier of your phone;
data held by a hospital or doctor, which could be a symbol that uniquely identifies a person.
a company registration number;
an email address such as info@company.com;
anonymized data.