Envo is an acronym for "Environment Ontology".
The term "ontology" is defined as the nature and relationships between real world objects or concepts.
In the case of EnvO, this is an open or community developed ontology or controlled vocabulary intended to standardise descriptions of environments associated with SSOs (samples, specimens and observations).
Notable users of this ontology include University of Pennsylvania (Beta Cell Genomics database), University of Montpellier (Modeling, processing and analysis of large scale data in biology, health, agronomy and environment) and University of Oxford (ISA) among many others.
To get more information, the official website can be found here...