Topic says it all! I have no idea what a trill is. Also, how would you play a trill? The song crazy train (im learning) has a trill in it .
I think that its essentially a very fast series of hammer on's and pull offs. Just keep going til your fingers get up to speed.
A trill is rapid alternation between two notes. On your guitar you'll know that as 'hammering on and pulling off really fast' between two notes.
It's essentially a tremolo. It's the rapid repeated change between two notes.
Two notes playes in quick succession. An example would be

You'd just hammer on and pull off between the two notes quickly.
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Quote by JMack
It's essentially a tremolo. It's the rapid repeated change between two notes.

No, I don't believe it is.....
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Quote by nightwind
No, I don't believe it is.....

i think tremolo is technically a change volume but you know what he ment
it's basically hammering-on and pulling-off as fast as you can.

(tr 6)
eg. -----5------- would be like ----5h6p5h6p5h6--- etc.

a good example i can think of that uses a trill is War Pigs by Black Sabbath at around 1.34


yea why not. I can play up to and including the first fill fine, not perfect but im perfecting it :P. It's not like i had trouble playing it, but i was just curious what a trill was so i could learn it and in turn play it better.
play this really fucking fast.

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Yeah, I THINK there is a trill on the intro to "The Trooper" on the part where it's like 8p7h8p7h8p7h8
Trills are used extensively in classical music, not so much in popular music. It's essentially the rapid alteration (generally the 8th multiple of the beat value -- 4/4 = 32nd note trills, 8/8 = 64th note trills -- unless otherwise specified) between two notes, it's not necissarily hammer-ons and pull-ofs, nor is the difference necissarily a chromatic semitone (although it usually is). It's marked on shet music as tr. followed by a squiggley line (~~~).