2) don't understand the end of the taxiway end and runway beginning is defined by the hold lines,
Small point but I think that you will find that the end of a taxiway is where the taxiway and the runway join i.e. at the physical edge of the runway.
Taxiway holding positions (holding points) are designated (marked) to ensure that the largest aircraft for which the aerodrome is designed holding at the most adverse angle does not infringe a myriad of obstacle and / or signal critical areas.
Asking a pilot to hold short of runway(nn)
assumes that the pilot knows the design standard of the aerodrome, the aerodrome category, the physical limitations and the signal in space limitations not to mention the wingspan of the aircraft about to roll combined with the pilot's ability to maintain the centerline.
Bit of a big ask!!
Hence the reason for holding points (position).
"Filthy 1234, are you ready?". "No, waiting on the cabin" AAAAARGGGHHHH!!!!! What's wrong with the correct "Negative"? What kind of idiotic gloop-speak is "waiting on the cabin"? Are you serving the cabin tea? Do cabins even drink tea? Just "Waiting for the cabin" would be bad enough, but on it?
Ah Ha, I can see that in expecting you to have a basic understanding of the issues involved in getting a commercial flight in the air, I have been placing your understanding on too high a level.
Please think of "just waiting for the cabin" to mean that we have the tug, driver, engineer, release from ops and you might see that everything has been removed from the aircraft including the airbridge but we are not yet ready because.......so even if you don't know how long that is going to take if you tell the aircraft waiting for this stand what we said then atleast they will understand.....................just like when we say "request FL380" and you respond with "NO".........in a team environment, it helps to know why i.e. we do not object to (we prefer) "FL380 not available doe traffic" or "FL380 not available due to military restriction" etc.