Scordatura literally means 'mistuned'; it refers to any unusual tuning of an instrument.
The harp is normally tuned with seven strings in each octave, with strings repeating at the octave. Thus, either all the C's are natural, or all the C's are sharp. By breaking this rule, and tuning a particular note name differently in different octaves (e.g. an F natural below middle C but an F sharp above it), we can find tunings that make certain kinds of music feasible on a single-row harp without levers or pedals.