The Sector Vocabulary codelist contains this value: Humanitarian Global Clusters. This value only exists in the IATI universe. I found out because I was looking for a French translation, and could only find this specific phrase on the IATI site.
“Global cluster” seems to designate a sector for coordination purposes.
The url provided in the codelist rather leads to the HDX website; the words used there are “humanitarian cluster names and codes”, with the source being the UN Office for the Coordination of Humanitarian Affairs (rather than the Inter-Agency Standing Committee).
I would suggest to correct this entry in the codelist to reflect the codelist nature and owner more accurately.