CIGESMED relies on the following thesaurus definition (ISO 25964-2011): controlled and structured vocabulary in which concepts are represented by terms, organized so that relationships between concepts are made explicit, and preferred terms are accompanied by lead-in entries for synonyms or quasi-synonyms.

 Thesauri are therefore a category of documentary languages among others. The terms are linked by synonymy relationships (equivalent term), hierarchy (generic and specific term) and association^? (related term); each term belongs to a category or field.
 A thesaurus is a linguistic tool to link the natural language of users and that contained in the resources. It overcomes the limitations of natural language, very rich but often ambiguous.
 A thesaurus makes possible to avoid the risks induced by synonyms, homonyms and polysemies present in natural language. It only incidentally provides definitions, relationships of terms and their selection outweighing the description of meanings.

Bottom-up initiative on a microthesaurus focused on coralligenous habitats