What exactly is a permanent cookie?
We often receive questions like "what a permanent cookie is and whether it is considered a technical cookie" so here comes a bit of clarification on what is an intersection between the technical and legal jargon.
Permanent cookie is simply a technical name for any HTTP cookie (RFC 6265 set to never expire in the user browser. From the practical perspective, we would also consider "permanent" cookies with expiration time set far in the future — say one year, five years etc.
And that's really it as it comes to "permanent cookies". Please note this definition doesn't say anything about its purpose, and it's because cookie's lifetime is orthogonal to its function, and this is what the "technical" or "strictly necessary" language (GDPR) applies to.
In real-life applications a long-term (permanent) cookie can be used for many purposes, from storing your language or currency preferences on a train booking website, or your "remember me" authentication information (technical or "strictly necessary" cookies) to keeping your unique user identifier for behavioural profiling purposes (advertising cookie).