Huge number of people gather in auditorium (5)
I believe the answer is:
horde
This could be a double definition.
'huge number' is the first definition.
'horde' can be an answer for 'number' (thesaurus). I am unsure of the 'huge' bit.
'people gather in auditorium' is the second definition.
'horde' can be an answer for 'people' (I have seen 'Many people' mean 'horde' so perhaps 'people' could also mean 'horde'). I am not certain of the 'gather in auditorium' bit.
'of' is the link.
Can you help me to learn more?
(Other definitions for horde that I've seen before include "Large army" , "Huge noisy crowd" , "Large force" , "Throng, mass" , "A swarm or multitude" .)