The concept of essential biodiversity variables (EBVs) was proposed in 2013 to improve harmonization of biodiversity data into meaningful metrics. EBVs were conceived as a small set of variables which collectively capture biodiversity change at multiple spatial scales and within time intervals that are of scientific and management interest. Despite the apparent simplicity of the concept, a plethora of variables that describes not only biodiversity but also any environmental features have been proposed as potential EBV (i.e. candidate EBV). The proliferation of candidates reflects a lack of clarity on what may constitute a variable that is essential to track biodiversity change, which hampers the operationalization of EBVs and therefore needs to be urgently addressed. Here, we propose that an EBV should be defined as a biological state variable in three key dimensions (time, space, and biological organization) that is critical to accurately document biodiversity change.