Glossary
nftables
The modern Linux kernel framework for packet filtering and firewalling, replacing iptables with a unified rule syntax and tooling.
nftables is the current Linux packet-filtering framework, the successor to iptables. Using the single nft tool, it organizes rules into tables and chains and handles IPv4, IPv6, NAT, and more with one consistent syntax, replacing the separate legacy tools.
For hardening it is the layer where you enforce a default-deny firewall, allowing only required inbound services and limiting outbound traffic. Rulesets are typically stored in /etc/nftables.conf and loaded at boot, giving a reviewable, atomic configuration.