fstab

defaults = rw, suid, dev, exec, auto, nouser, and async.

sync/async              All I/O to the file system should be done (a)synchronously.

auto                    The filesystem can be mounted automatically (at bootup, or when mount is passed the -a option). This is really unnecessary as this is the default action of mount -a anyway. 

noauto                  The filesystem will NOT be automatically mounted at startup, or when mount passed -a. You must explicitly mount the filesystem.

dev/nodev               Interpret/Do not interpret character or block special devices on the file system. 

exec / noexec           Permit/Prevent the execution of binaries from the filesystem.

suid/nosuid             Permit/Block the operation of suid, and sgid bits.

ro                      Mount read-only.

rw                      Mount read-write.

user                    Permit any user to mount the filesystem. This automatically implies noexec, nosuid,nodev unless overridden.

nouser                  Only permit root to mount the filesystem. This is also a default setting.

defaults                Use default settings. Equivalent to rw, suid, dev, exec, auto, nouser, async.

_netdev                 this is a network device, mount it after bringing up the network. Only valid with fstype nfs.