(music) the sound property resulting from a combination of organ stops used to perform a particular piece of music; the technique of selecting and adjusting organ stops WordNet 3.0 & Open English WordNet

Registration is the technique of choosing and combining the stops of a pipe organ in order to produce a particular sound. Wikipedia

The art of combining the different sounds of a pipe organ to produce the desired sound Wikipedia Disambiguation

An instance of or a certificate attesting to the fact of entering in an official list various pieces of information in order to facilitate regulation or authorization, including one's name, contact information and, in some instances, data concerning a specific possession or property. OmegaWiki

The art of selecting and combining the stops or registers of an organ. Wiktionary