The simplest explanation is that a GEDCOM is a file of data downloaded from a genealogy data base in a standard format. The data can then be uploaded to another genealogy data base which recognizes the GEDCOM standard, making it possible to transfer information between otherwise incompatible data bases. In the case of Wikitree, there is an intermediate process called GedCompare where the file is compared with existing Wikitree records before the data is uploaded to Wikitree profiles.
