UCD1+ controlled vocabulary - Updated List of Terms Version 1.4

This document describes the list of controlled terms building up the corpus of the Unified Content Descriptors, Version 1+ (UCD1+).

The document describing the UCD1+ principles can be found at the URL: https://ivoa.net/documents/UCD1+/20180527/index.html. It is an IVOA Recommendation. The process to maintain and enrich the UCD list of terms is standardized in https://ivoa.net/documents/UCDlistMaintenance/. It states that successive versions of the UCD1+ vocabulary are distributed in Endorsed Notes within the IVOA. This version is the first Endorsed Note for UCD list, currently proposed. It contains new UCD words discussed and accepted by the Semantics Working Group during the UCD list v1.3 RFM (request for modification) available at https://wiki.ivoa.net/twiki/bin/view/IVOA/UCDList_1-3_RFM.