Personally identifiable information (PII) is any information that can be used to identify an individual person. PII can include a wide range of information, such as a person's name, address, phone number, email address, date of birth, social security number, or any other information that can be used to identify an individual. In the context of online advertising, PII is often collected and used by advertisers and publishers in order to deliver relevant and personalized ads to users, and to measure and optimize the effectiveness of an advertising campaign. PII can be an important part of an advertiser's marketing strategy, as it can help to build a database of qualified and engaged leads, and to deliver relevant and valuable messages to the user. PII can also be sensitive and valuable information, and it is important for advertisers and publishers to handle and protect PII in a responsible and transparent way.