Stanford encyclopedia of philosophy - fail

The problem with defining sense-data as "private, non-physical entities that actually have the immediately experienced sensory qualities" is that, to me, this is very obscure.
I have a bit of a general gripe with the authors that Stanford ask to contribute to their philosophical encyclopedia. They seem to me to fail properly to define the new terminology which they introduce, which surely is the key purpose of an encyclopedia.
The above definition says that a sense datum is an "entity". According to the OED, an entity is a being, a thing that has real existence. It seems confusing to define sense data as both non-physical and entities. Are they some form of metaphysical entity?
BonJour goes on:
"For a variant usage of this term, see Moore 1953, who there uses the term “sense-datum” to stand for whatever it is that is immediately experienced or given, possibly even a public physical object, and then argues somewhat tentatively that the entities that actually have this status are sense-data in the more usual sense, rather than physical objects.)"
Does that make any more sense? I am still struggling.
The Stanford article on 'Sense-Data' by Huemer suggests that they may be "mental images". The proposal that what we perceive are mental images is, to say the least, contentious.
The Huemer article goes on to try and give a "Stanford" view of what sense-data are (consistent with BonJour) as follows:

1. Sense data are the kind of thing we are directly aware of in perception,
2. Sense data are dependent on the mind, and
3. Sense data have the properties that perceptually appear to us.

1. This distinguishes between direct and indirect perception, which is helpful but does not describe sense data.
2. Obvious (I think)
3. Meaningless
So I am still looking for a description of sense-data that actually describes what they are. The article proceeds to widen the definition as follows:
"The term “sense data” has not always been used in the sense described above. Indeed, when the term was first introduced by early 20^th-century philosophers such as H. H. Price, G. E. Moore, and Bertrand Russell, it was intended only to denote that which we are directly aware of in perception."
But you will note we still don't know what they are. Isn't this a bit like saying "smells are what we smell" or "sounds are what we hear", it fails to provide a definition. The article then goes back to the original definition for the arguments for and against, which I think is a bit premature.