Zero Trust
A security model that grants no implicit trust from network position, and authenticates and authorises every request individually.
The model it replaces is the perimeter: a hard boundary with a trusted interior. That failed for two reasons — the interior turned out to be reachable via phishing, supply chain and VPN compromise, and there stopped being an interior once workloads moved to cloud and staff worked from anywhere.
Zero trust says: every request carries an identity, every request is authorised against policy, the decision considers device posture and context as well as identity, and the principle of least privilege applies to service identities as strictly as to human ones.
In practice this is strong workload identity (mTLS or signed tokens between services), short-lived credentials rather than long-lived keys, per-request authorisation rather than network ACLs, and segmentation so that a compromise reaches one workload rather than a subnet.