The **Unified Medical Language System (UMLS)** is a system developed by the **U.S. National Library of Medicine (NLM)** to integrate various medical terminologies and facilitate interoperability between different healthcare information systems. It consists of three main components:

1. **[[Metathesaurus]]**: A vast database that consolidates millions of medical terms from different sources (e.g., SNOMED CT, LOINC, ICD-10, MeSH, etc.) into unique concepts with standardized identifiers.

2. **Semantic Network**: Defines semantic relationships between concepts in the Metathesaurus, helping structure and organize medical knowledge.

3. **SPECIALIST Lexicon & Tools**: Provides natural language processing (NLP) tools for biomedical text processing.

UMLS is widely used in medical [[research]], clinical software development, [[electronic health record]]s (EHR) processing, and AI applications in healthcare.