In analysing meaning Ogden and Richards created a three part model of symbol (language), reference (concepts) and referent (objects). This is a useful way of looking at things. One can think of there being an object, a person, for example, and distinguish the person (object) from the thought of the person (concept) and the term ‘person’ (language).
In other words, there are three ‘entities’ in order to discuss this one object. That which is in the mind are the concept and the words that represent the person.
The concept of entity helps to show the mind as holding three separate “objects” to talk of one real thing.
Entity also helps us understand how we are able to talk about non-real “things”.