Users with unprivileged credentials who properly execute "sudo" (for example) to perform authorised administrative activities are also "escalating privilege". It is not only an exploit or a bug.

There are many examples of a user's or process's privileges being elevated/escalated by design. - sudo in general - GitHub's "sudo mode" - https://en.wikipedia.org/wiki/Setuid:

They are often used to allow users on a computer system to run programs with temporarily elevated privileges to perform a specific task. While the assumed user id or group id privileges provided are not always elevated, at a minimum they are specific.

Generally speaking, privilege escalation means getting more rights in the system than you already have.