Noun

1. A set of labels applied to the various objects in a system.
   • 2009 January, Bernard Russo and James J. Tattersall, "Program of the Sessions: Washington, District of Columbia, January 5–8, 2009", Notices of the American Mathematical Society, 56:1^{http://www.ams.org/notices/200901/}, page 143:

     4:00PM (722) An upper bound for the number of graceful labelings of a path with n edges. Sylvia R. Naples, Bard College

2. The introduction of a traceable chemical group (e.g., containing an isotope or a fluorescent dye) into a protein or other biomolecule of interest so it can be tracked or quantified during experimental analysis.
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