An entity is a kind of abstract species that can be used in formation reactions.
Each entity gets the following variables:
<entity>.logact (log activity for aqueous species, intensity for other entities) <entity>.con (entity concentration in its home phase)
and furthermore for each system phase:
<entity>.<phase> (cumulative mass balance for primary entities, contains mass of all derived entities in all child phases in units of indicated phase) <entity>.<phase>.con (individual entity concentration in units of given phase)
Derived forms of entities are: species, gases, minerals, sites, solid solutions, electrostatic planes etc.