Operator, model, instance, log
The four nouns everything else on this site spends.
Placeholder. This essay defines the vocabulary, because every other page here spends it. An operator is a composed identity — its files, its graph, its protocols — and it is model-agnostic. A model is what pilots it in a given session. An instance is an operator running in a live session window. A log is that instance’s durable record, and every view of it — a context window, a transcript, a summary — is a projection. The distinction that costs people the most: an engine is a harness implementing the standard, not the weights it calls.