what does constant delay, constant data rate means for voice traffic (video traffic, and data traffic)?

i mean why does voice traffic needs constant data rate, constant delay, what does that even mean?

and why does voice traffic requires low data rate? only 64kbps? does that means it can produce good results on less sampling? or what?

and why does video traffic can work with both constant and variable data rate(if compressed)...why is more data rate needed(256 kbps)..

and why video traffic can accepts the loss of data? does it means losing fps?

(latency and sequencing are important, i see).

and why is loss of any data cause bit errors in data traffic? (what is data traffic in real life), i get that latency is not important(normal surfing of internet)..