According to Longman dictionary (and also Oxford dictionary), a parking ticket is "an official notice fixed to a vehicle, saying that you have to pay money because you have parked your car in the wrong place or for too long".
I don't know what is the right word for the piece of paper you get from a parking meter. Can we call it a parking receipt or a parking permit?
Best Answer
As per the comments, you are looking for a name for the piece of paper that proves you have permission to park, not a piece of paper that proves you have paid money.
Receipt
"Receipt" is not correct then. The OED defines a receipt as:
That is not what you're looking for. Even if the "permission" also prints the details of a receipt, that does not make "receipt" a correct definition for "a piece of paper that gives permission".
Similarly, the invention of the spork has not made the words "fork" and "spoon" freely interchangeable. For the same reason that a fork is not the same as a spoon (even though sporks exist), a receipt is not a piece of paper that proves you have permission (even though both are sometimes printed on the same piece of paper).
Ticket
When talking about a document that proves you have permission, I would instinctively call it a ticket:
However, we run into a problem here. "Ticket" is ambiguous, since it could also refer to a fine:
In the interest of avoiding misinterpretation, I would not use "parking ticket". While it is technically correct (through the definition of ticket), it will predominantly be understood to be a synonym for "parking fine".
Permit
Permit fits the bill:
However, there is an ambiguity. There are two sorts of parking permits:
Again, we find ourselves with a contradiction. When you say "I have a parking permit", it is possible for people to understand that you have a long term permit which exempts you from having to have a short term parking permit.
Permission
Instinctively, I would have said that this is incorrect. Permission refers to the abstract concept of being allowed to do something, rather than the physical proof of permission.
However, the OED disagrees with me:
I could make the same argument about ambiguity. "Parking permission" could refer to either the abstract concept of being allowed to park, or the physical document that proves you're allowed to park.
I would expect most people to initially understand the former (the abstract concept), while you are focusing on the physical document.
However, my argument seems weaker in this case (compared to the others). The distinction between the abstract concept and physical object can usually be derived from context, and can even be irrelevant in some cases.
Technically, you have both. Because you have the physical document, you therefore also have the abstract concept.
This makes it obvious that you're talking about a tangible item, thus excluding the possibility of people inferring you mean the abstract concept.
Parking permission is a valid option. Out of all the listed options, it has the least chance of being misinterpreted.
In practice, I find usages of "ticket" but not "permission"
I've resorted to Googling, hoping to stumble on usage of the words. This is the best I could come up with. The system is called "Pay and Display". But when you read though it, you can see that "ticket" is the preferred word:
For a second, I though I had found an answer when I saw coupon parking mentioned. However, that doesn't fit your current scenario:
Again, no luck in finding a word to use that does not create ambiguity.
Conclusion
You get to choose which one you use, in my opinion. There is no strictly defined answer here.
Parking permission seems to be the best choice from a semantical point of view. Out of all the presented options, it has the lowest chance of being considered too ambiguous.
Ticket is also a good choice, when you observe the practical usage based on what I have found. So it wouldn't be wrong to use "ticket".
However, I do want to urge you that you should still avoid using "parking ticket" (because people will assume you mean a parking fine); and that you should endeavour to make it clear from context that you are talking about a permission, not a fine.
Many people will infer you mean a fine, most likely a parking fine. It is very ambiguous.
The context makes it clear that you're not talking about a fine. This isn't ambiguous, due to the context you've used it in.