Terminology constraints are predefined lexical rules in natural language processing and text generation that mandate the inclusion or exclusion of specific words, phrases, or domain-specific terms in a model-generated output. Commonly applied in neural machine translation, structured data-to-text generation, and controllable text synthesis, these constraints ensure that specialized vocabulary, standardized nomenclature, or brand names are accurately preserved rather than replaced by generic alternatives. Generative language systems typically enforce terminology constraints during the decoding phase using specialized search heuristics, finite-state automata, or constrained optimization techniques to satisfy the required lexical rules without sacrificing the grammatical fluency and contextual coherence of the resulting text.