In my limited understanding, Ignorance is any holding onto an absolutist/fixed view of things. This view is commonly referred to as "dualistic" or "extreme". One should not see things as being either one or the other. This is why the Madhyamaka philosophy was developed, the school of the "Middle Way". This school proposes that any fixed view should be eradicated with emptiness, the realization that all things lack independent existence. So things are neither high nor low, big nor small, black nor white. Nagarjuna said that even dwelling in "the middle" is a fixed view, so therefore we should not hold any presuppositions whatsoever. Likewise, Buddha Shakyamuni says in the Pali Canon that even a man who claims to be equal to all others is holding onto a fixed view that needs to be dispelled. And since Ignorance is the first link in the 12 links of interdependent origination, if we free ourselves from ignorance we will be free from the sufferings of Cyclic existence. This is why Je Tsongkhapa says that the root of suffering needs to be cut out with the sword of wisdom.
Of course, a mere intellectual understanding of this is not sufficient to set ourselves free from suffering, which is unfortunately all I have gained!! The great masters say that direct realization is required in order gain liberation. So once one can dissolve the self and all phenomena through emptiness, and see the freedom and vastness of things, then you are truly awakened. Of course, this sort of experience is beyond all conception. This is why Nagarjuna explains that the true nature of things is: Not existing, not NON-existing, Not BOTH and Not NEITHER. Once you have truly transcended all of these false views, then you can be said to have realized the Dharmakaya.
Even if one observes modern science, you can see these realizations taking place. The theories of Classical physics (starting with Sir Isaac Newton) all claim that the Universe can be organized and defined in a set of unifying laws and principles. These theories implied that once you knew "all" of the rules, that you could explain every single thing in the universe. This was often referred to as the Mechanical view of the universe.
However, modern Quantum physics is discovering that nothing can be absolutely known for sure. These theories are describing the universe in "Probabilities" rather than in absolute laws. They have discovered that the closer you examine objects, the more unstable they become. For instance, you can look at a table and it appears to be still and uniform. But the closer you examine it, the more you notice that it is composed of molecules in constant motion, all separated by space, yet still connected through energy and force. Even these molecules can be broken down further, with what science is now calling "String Theory". It is truly amazing how much these findings correlate with the Ancient Buddhist Philosopy.
I hope some good has come from my rambling! I enjoy very much discussing and contemplating these kinds of topics.
Blessings to all!