In several contexts I will refer to a "property" of something.
A property is anything you can "set" for that something… for instance, if you have three resistors in your design, they are likely to be called "R1", "R2" and "R3". Those would be the values' for the resistors' "reference" property.
When you reach the stage of making your own schematic symbols, you will have to give each pin in the schematic symbol a number, so "number" is one of the pin's properties.
And so on.