This article is from the Star Trek Tech FAQ, by Joshua Bell inexorabletash@hotmail.com with numerous contributions by others.
According to the Tech Manual, it's a measure of subspace distortion
named after Zefram Cochrane, the inventor of warp drive. 1 cochrane is
the distortion required to propel a ship at Warp 1, so field strengths
are typically measured in millicochranes. It's shown up on TNG a
couple of times amidst Geordi's technobabble.
 
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