A Persistent Identifier is a kind of number plate that we wear in the web. After all, we use PIDs on a daily basis in our analogue world, such as when we are asked for our identity card number. Only here we are on the web. Fortunately behind a Persistent ID there is an organization that ensures its persistence over time. At this point someone might reply that the address of a website is a persistent ID. Wrong, because behind it there is not always an association to ensure its long-term durability.
A PID is “a code which remains constant as a means of identifying a digital object regardless of changes to its location on the internet”.