labeling

Short definition from Wiktionary

Noun

1. 1
   A set of labels applied to the various objects in a system, to packaged goods, and so on; the act or process of applying them.
2. 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.

Verb

1. 1
   present participle and gerund of label