Re: Quartus prime - what is the definition for unused pin?
There are different defualts. Unused pins have a default behavior(such as tri-stated with weak pull-up). This is more of a behavior, whereby if you have an output pin in your design but don't make any IO standard assignments, it will still behave like an output pin, and the defaults affect the what IO standard it is.
For pins in the actual design, it is good practice not to rely on defaults at all and assign the standard to all of them.