An identity card or identity document is a document that uniquely identifies a citizen of a country. This is tied to an identity number, a unique serial number for the person. Unlike a passport, that is recognised around the world, and allows a person to travel internationally, an identity document is generally intended for use within the country. It can be a useful means of confirming your identity for official purposes, such as confirming age or opening a bank account.
A driver's license is another common form of identification in many countries, however not all citizens will have one. Likewise passports. In countries with an identity document, it is generally the case that every citizen of any age will possess one.
In some countries the driver's licence is not a separate document, but a page of the identity document.
Some countries have legal requirements for citizens to carry their identity document at all time. This is sometimes seen as a repressive, police state practice, since it is intended to facilitate policing.
For instance, in South Africa in the Apartheid era, all citizens except those who were European had to carry a "passbook" or identity document, to facilitate their policing. (Act No 67 of 1952) A person found without a passbook could be seized and deported to a bantustan or jailed. This law was unpopular, with passbook-burnings featuring at many protests.