Voltage ratings are in the 'It depends' category.
For most devices, you should read the data sheet for the specific statement of just what the voltage rating implies. For some parts, the rating is understood to mean specific things.
The voltage rating of an electrolytic cap, for instance, is usually taken to mean it's rated 'Working Voltage' - i.e. the voltage it can withstand continuously in normal operation (although I would never use a 10V electrolytic in a 9V system...)
For semiconductors, it may mean the normal (highest) rated working voltage, or (depending on context) it may mean the absolute max rating.
So the answer is - find a voltage rating that you are unsure of, read the datasheet, and if it's still not clear, ask - someone here should know what it means.
Your LED rating may refer to either it's maximum forward voltage drop (probable) or it's reverse voltage rating (possible but unlikely).
Cheers
PeteS