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In zoology either it is a (commonly used?) misinterepretation or misidentification of a species name:
Musca complexa Linnaeus, 1758 sensu auct.
Musca complexa Linnaeus, 1758 misident. sensu auct.

Misidentification basically means that there is a type (or other material) that can pinpoint the exact identity of the species.
If such material does not exist it truely becomes a matter of interpretation of the description. In that case there can be opposing opinions and than you may have two 'species':
Musca complexa Linnaeus, 1758 sensu Fallén, 1810
Musca complexa Linnaeus, 1758 sensu auct. non Fallén, 1810