For questions about selectivity between different functional groups.

As defined in the IUPAC Gold Book (DOI:10.1351/goldbook.C01051):

Chemoselectivity is the preferential reaction of a chemical reagent with one of two or more different functional groups.

A simple example is the reduction of a ketoester with sodium borohydride, which only reacts with the ketone, but not the ester:

Chemoselective reduction of ethyl acetoacetate with sodium borohydride

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