The quality or state of being perplexed or puzzled; complication; intricacy; entanglement; distraction of mind through doubt or difficulty; embarrassment; bewilderment; doubt.

Perplexity is a measurement in information theory. It is defined as 2 raised to the power of entropy, or more often as 2 raised to the power of cross-entropy. The latter definition is commonly used to compare probability models empirically.