What does 'hard stuff' mean?

[Igor]

Test No. incompl/inter-54 "Lots of Stuff", question 3

He'd carefully avoided having any alcohol until he was twenty-five and then he had a small drop of the ......... stuff.

(a) hard
(b) difficult
(c) solid
(d) ground

Test No. incompl/inter-54 "Lots of Stuff", answer 3

He'd carefully avoided having any alcohol until he was twenty-five and then he had a small drop of the hard stuff.

Correct answer: (a) hard

Your answer was: correct
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Hi! What does it mean?
Hard stuff
Thanks

[Alan]

Hard stuff is strong drink.
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English as a Second Language
You can read my ESL story A day in the life of a flat hunter