ACCEPT #
Let the packet through to the next stage of processing. Stop traversing the current chain, and start at the next stage.
DROP #
Discontinue processing the packet completely. Do not check it against any other rules, chains, or tables. If you want to provide some feedback to the sender, use the REJECT target extension.
QUEUE #
Send the packet to userspace (i.e. code not in the kernel). See the libipq manpage for more information.
RETURN #
From a rule in a user-defined chain, discontinue processing this chain, and resume traversing the calling chain at the rule following the one that had this chain as its target. From a rule in a built-in chain, discontinue processing the packet and apply the chain’s policy to it.