Aside from alternating current and direct current we already know, do you still other type of current flow? Also, is it for that type of current flow to exist? or there are only 2 types of current flow in this universe (ac,dc)
In the DC/AC class there's nothing else. The criterion is frequency, and that can be zero (DC) or non-zero (AC).
Current is displacement of electrical charge, and that can be in different forms: electrons carry a negative charge, but cations for example a positive charge, so cations going the same direction as electrons will have a current with reverse polarity. That's another way to look at different kinds of current, but has nothing to do with the frequency.
So it's just AC and DC.
The way I get it, AC and DC are the names of two very specific current flows. They are named, because they are used by far the most often.
Forier transform is a mathematical method to represent any "good" function as a sum of a constant, sines and cosines. That is, any function, e.g. current, can be expressed as a combination of DC and (in)finitely many AC-s with different frequencies and ever smaller amplitudes. This could point out that there is only DC and AC.
However, this transform is not unique. Any set of "independent" (orthogonal) functions can be used as a base to decompose the original signal. Then there is "no" AC and DC.
Why do we use the Fourier decomposition so often? One reason is that sinusoids occur often in physical nature and thus are intuitive.