Is true black possible? Black is the absence of light because it absorbs light, but when we create black paint or black objects, light is always reflected, either in all directions in matte or smoothly in shiny black objects, making it never a true black. Would it be possible to use polarization to create an object that does not reflect any light, creating a truly black substance, without any shadows or reflection of light?
 A: The only thing I can think of being true black would probably be a black hole. As light does not bounce off a black hole.
A: The problem with the suggestion of using polarization is that you now have the reflections off the polarizers to contend with. 
I think the short answer is "it depends on how 'black' you want it to be". "Truly black" = reflectance of 0. I am quite sure that is impossible - there will always be some probability of light scattering off a surface. All you can do is make that probability "quite small".
The world record for "blackness" appears to be held currently by Ventablack, a material with a special surface structure (nanotubes) that traps incident photons, and reflects less than 0.04 % of incident light. That is indeed very nearly black (but nowhere near "perfect"). Just look at this picture to get a sense of just how black that is. Of course if most cameras have 12 bit sensors, then one LSB is 1 part in 4000 - and 0.04% is 1 part in 2500. So indeed, this is almost invisibly black for a typical camera. Uncanny.

(Image from the above linked source).
A: Just to add to the above answers, and since to did not limit your question to the visible range - if you define black as absence of light (photons emitted or reflected), then there is no such substance, because according to black body radiation model, everything with a temperature above absolute zero (which is essentially truly everything in the universe:) radiates, meaning it's always emitting photons, and thus is not black. 
A: A true black surface would need a temperature of 0 Kelvins as anything with heat will have excited electrons and will emit photons. However, dark matter is an example of purely black matter it only means that dark matter does not consist electrons.
Theoritically, a purely black object would be one that does not radiate light or absorb light. As absorbtion of any kind of light also brings along with it heat which again hypes up the electrons. Hence, it is impossible, even theoritically for an object to be purely black.
