User nobody on a Unix system is traditionally user id 65534. This user is used by NFS servers when they cannot trust the client-supplied uids and gids, or when the root-squash option is being used.
See https://www.kernel.org/doc/ols/2006/ols2006v2-pages-59-72.pdf and https://www.oreilly.com/openbook/linag2/book/ch14.html for more information on user nobody.
Some misguided programs or guides suggest that this user should be used for untrusted program execution or handling untrusted data. This is bad advice. Services should have their own, dedicated, user account. Even on sites where NFS is not being used, processes run as user nobody or files owned by user nobody may grant far more privileges than expected, especially if two services have been misconfigured in this fashion.
Do not use the user nobody for anything. It is for NFS.