PQL — who are you?

I have been reading about PQLs i.e. Product Qualified Leads and have realized that there is quite some mis-understanding about what it is. As the name suggests PQLs are those accounts that have tried the product & have reached a stage of initial value.
Even though it sounds like a “try before buy” model, PQLs are much more than that. Anyone who signs up for a free trial of the product is not a PQL. Nor is someone using the free version in a freemium model. A PQL has to be a user who has experienced a certain level of success with the product.
If we were to consider LinkedIn Premium as an example, not every free trial of a premium account is a PQL. Only accounts that have witnessed significant gain in value during the trial phase would qualify as a PQL. Simmilarly for Spotify Premium, PQL metrics could be number of tracks played or playlists saved. Hitting a usage limit — like exhausting the number of free reads on Medium is another example.
Defining & tracking PQL metrics are very closely linked to how a product adds value to a user persona!