Deterministic
A process is deterministic when the same input always produces exactly the same output. Hand-written rules are deterministic: a program that adds a past-tense suffix to a verb will do it the same way every time, and you can read the rule to know in advance what it will do.
This is the opposite of how most modern language models behave. A large language model is probabilistic: it samples from many possible continuations, so the same prompt can yield different answers, and there is no rule you can point to that explains any particular one.