What does "balanced triodes" refer to as related to vacuum tubes?

Spot on Mulveling....   I will now pay a few extra bucks for matched triodes with dual triode small signal tubes.    They are almost always more uniform,  and test better than just buying un-matched/ un-graded tubes.     

I bought a Hickok tester in August and it was an eye opener.   Tubes from trusted sources were as advertised.   Ones bought in a pinch locally turned out all over the map.    Especially any bought from guitar shops.  Since getting a tester I am pretty confident that music stores get every one else's junk.

Thanks to all for the informative responses.

Thanks, @mulveling  , that was particularly helpful. 

wouldn't it be great if audiogon had 'stickies' for basic knowledge such as this...?

@mulveling +2

@mulveling - Very well said!