What exactly is a Specification?

Question

I read or hear sentences such as:

The Java Persistence API (JPA) is a Java application programming interface specification...

or

Answer 1

I think the key idea here is "specification doesn't include an implementation."

When Sun was the steward of Java, they would write specifications for features like Java EE and JPA, giving other vendors the freedom to implement as they wished. Sun would usually have an implementation of their own with which to compete, but their goal was to sell hardware. Encouraging other vendors to provide competing implementations only furthered that aim.

Sun's specifications would come with neither code nor JARs; they were prose descriptions of how the code would work.