Old lady hosting company event is hot stuff (5)
I believe the answer is:
magma
'hot stuff' is the definition.
(I've seen this before)
'old lady hosting company event' is the wordplay.
'old lady' becomes 'ma' (both can mean mother).
'hosting' indicates putting letters inside (inserted letters are welcomed in or hosted).
'company event' becomes 'agm' (I can't explain this - if you can you should give a lot more credence to this answer).
'ma' going around 'agm' is 'MAGMA'.
'is' is the link.
Can you help me to learn more?
(Other definitions for magma that I've seen before include "Hot molten rock" , "hot stuff" , "That's hot!" , "Molten or pasty rock" , "hot filling in crust" .)