Block on the Periodic Table?

What are the blocks of the periodic table? What is the purpose of naming the elements per block group? What do they signify?

Below is a picture of the 4 blocks in the Periodic Table. The elements in a block all use the same orbital to hold their valence or outer shell electrons. For example, all of the elements in block 1 have their valence electrons in an $\ce{s}$ orbital, those in block 2 have their valence electrons in a $\ce{p}$ orbital, block 3 the $\ce{d}$ orbitals and block 4 the $\ce{f}$ orbitals.