GedCom stands for Genealogical Data Communications. It is a way to download data from a genealogy program and then upload it to another venue. In other words, download genealogy data from your computer program or an Ancestry or other online tree and then upload it to another tree such as WikiTree.
The downside is that not all of the information is transmitted - such as media. And, when uploading to an online site such as WikiTree, each profile needs to be cleaned up as the sources do not upload in a desirable format. So, they have to be cleaned and made more readable.
I hope this helps explain it and there is more help here: