Mathematically it is where infinity enters into the equation. The idea first came into existence in n-n-physical reality with the idea of the Dao (opposites). Without duality you cannot have opposites. So you can think of a singularity as something opposites emerge from and into which opposites ultimately merge into. Energy is the medium.
Think of the opposites love and hate (which actually comes from fear). Hate drives apart and love draws together. Or electric charge. Electrons are needed to draw atoms together to make molecules, but strong positive charge (think free radicals) tear apart molecules. Both are properties of the Dao. Both make the physical world possible. Even dimensionality itself depends on it.