What exactly is a "No Objection Certificate" (NOC)?
In researching a potential trip in Pakistan on Wikivoyage I came across this term which is not well explained:
The visitor should be aware of the ever changing rules regarding sensitive areas and No Objection Certificates (NOCs), Note Verbals and other permissions and paperwork some in officialdom deem necessary for your to travel around the country. The most notorious NOC regulation is for foreigners to enter Kashmir, with the intention being so the security services can keep track (i.e. follow) foreigners to make sure they don't visit places they shouldn't. Outside Kashmir diplomats are the primary user of NOCs and theoretically the normal tourist should be exempt. However those in officialdom can view all foreigners with suspicion and demand an NOC when you step of a plane or out of a bus. NOCs need to be applied for through the Ministry of Interior, however if you are traveling on a non-diplomatic passport you should be fine - but its good to be aware of this nonetheless.
There is a Wikipedia article but it is very brief and not very well worded:
No Objection Certificate or popularly abbreviated as NOC is a type of legal certificate issued by any agency, organization, institute or in certain cases, an individual, that does not object to the covenants of the certificate. This certification is a requirement at most of the government-based departments predominantly from the Indian subcontinent..
Can somebody explain better than these sources what an NOC actually is? Is it a kind of permit?
In general, a NOC is a letter indicating the writer of the letter has no objection to the terms contained within said letter. Sounds very meta, but basically it's like saying 'I have no objection to what I'm writing about, and this is legal evidence stating so.'
Now why would that be useful? Let's take a common example.
A government employee wishes to take leave from his job and travel to the a certain country A from country B. To prove that he's able to leave his job temporarily, his department may issues a NOC to indicate that they're ok with him leaving for his 6 month holiday (which may raise questions in other cases due to its length) and that they're covering his leave. If he's a government employee, they may also issue a NOC to indicate that they're ok with him being issued a passport.
NOCs are also common in business, for example.
In this case, given the status of diplomats and the political impact they can have when travelling, and given their immunity status as well, it's often in a government's best interest to require NOCs to make sure that the home government of country B knows that the diplomat is travelling to country A, and that they're legally stating they're ok with what he's doing there. This also prevents country B from later claiming they had no knowledge of their diplomat's actions.
In highly politically-charged areas like Kashmir, it stands to reason that concern be even greater about tracking, noting and stating the intent of political activities, diplomats and emissaries.
However, Joe Tourist on the other hand, is usually not such a problem to countries. Of course, any concern or suspicion on their part would be nullified with an NOC, especially one from your employer stating that they, for example, know you're on holiday and are expected back at work in a few weeks.