I've always deeply admired Jay L. Garfield's stunningly beautiful translation of Nāgārjuna's Mūlamadhyamakakārikā or "The Fundamental Wisdom of the Middle Way." It is very demanding reading but will pay off especially if you have an analytic philosophy background. Garfield's translation is rigorous and precise - hence the effort needed to comprehend it.
Rather than babble about emptiness (Śūnyatā in Sanskrit), I think it is better to let other more qualified people give a description. Emptiness refers to our innate ability to see forms, patterns, events, possibilities and perspectives as they are rather than the way we'd like to see them. Chögyam Trungpa Rinpoche in "Cutting Through Spiritual Materialism" - another phenomenal book [:-)] - describes emptiness as: "So form is empty. But empty of what? Form is empty of our preconceptions, empty of our judgments. If we do not evaluate and categorize the maple leaf falling and landing on the stream as opposed to the garbage heap in New York, then they are there, what is. They are empty of preconception. They are precisely, what they are, of course! Garbage is garbage, a maple leaf is a maple leaf, "what is" is "what is." Form is empty if we see it in the absence of our own personal interpretations of it." [page 188]
Unfortunately, and because of the subtlety of emptiness, we can be misled. Emptiness does not mean that we should see - let's say - a physical world for what it is rather than our preconceptions of it. The problem here is that the very notion of a physical world is a concept and obscures the real world. And it does not help to equate emptiness with a Buddhist no-self position either since the concept of no-self is, er, just another concept.
As Garfield's translation gathers pace, he writes "The root delusion---the fundamental cognitive error---is the confusion of merely conventional existence with inherent existence. The realization of emptiness eliminates that fabrication of essence, which eliminates grasping, contaminated action, and its pernicious consequences." [page 248]
And this is followed by,
"That there is a self has been taught,
And the doctrine of no-self,
By the buddhas, as well as the
Doctrine of neither self nor nonself."
To neither the concept of self nor to no-self does there correspond an entity. These designations are conventional through and through and the mistake we keep making is trying to reify conventional designations. Garfield writes "To say neither self nor non-self is, from this perspective, not to shrug one's shoulders in indecision but to recognize that while each of these is a useful characterization of the situation for some purposes, neither can be understood as correctly ascribing a property to an independently existing entity. And if they cannot be understood in this way, what are we really saying?"
And almost immediately following this, he says "Nagarjuna begins to move toward his famous and surprising identification of nirvana with samsara, and of emptiness with conventional reality." [page 249]
If there are no entities lurking behind our conventional designations, aren't our conventional designations, er, merely conventional and empty of being ultimates? It is our tendency to reify conventions that causes problems, right?
Nāgārjuna's Śūnyatā is literally groundbreaking - sorry, sorry, couldn't resist - and paved the way for tantra and the realization of only Ati to emerge.