A base chain in nftables is attached directly to one of the underlying netfilter hooks (such as prerouting, input, forward, output, or postrouting), which allows packets traversing the network stack at that point to be evaluated against the chain's rules. A regular chain, by contrast, is not attached to any hook and can only be reached when explicitly called (jumped or goto'd) from another chain, functioning similarly to a subroutine used for rule organization.