What is the difference between Ceph and NFS when it comes to shared file storage?

We really expect question-askers to have done at least a bit of homework first to be honest, anyway here we go.

NFS is a file-sharing protocol, it doesn't define anything about the underlying filesystem at all, simply the protocol of how to access files on it.

Ceph is a distributed filesystem AND sharing mechanism, it defines how the data is stored on one or more nodes and presented to other machines for file access.

A single machine of any kind can be an NFS server, client or both, using whatever operating system and filesystem you like.

Ceph is normally used to 'bind' multiple machines - often hundreds if not thousands - to spread the data out across racks, datacenters etc. and to improve performance.

Oh and more of a personal opinion but NFS is very well known and mature, whereas Ceph is far from being new but isn't anywhere near as well known or mature.