Two questions in one. I'm looking at a schematic with two resistor symbols (unrelated to each other), with one having a value of zero and the other having a value of "NO-POP". What do these mean? If I had to implement their circuits, what components would I use?
NO POP means not populated (i.e. the space on the PCB is there, but there's no component). In this case you'd install nothing.
Zero-ohm resistors are used just for jumpers (so the same machinery can be used for jumpers and actual resistors). In this case you could use a jumper or a wire.
The "NO-POP" will stand for not populated, it means that when the board is loaded with components that part won't be placed / soldered. It's often used for optional components or as a form of link that may be used on one product variant but not another. Sometimes it can also be a "just in case" component where the designer isn't sure if the final product will require the component or not, but allows for it on the PCB in case so that the PCB doesn't have to be redesigned.
A zero ohm resistor is often used for similar purposes and is essentially a link that can be machine placed. You might find that different variants of the board will have it in place while others have it removed, or on some boards they can be removed by the user for different operation.