Block (periodic table)

A block on the periodic table is a group of elements that all have their electrons in the same atomic orbital. There are four blocks, s-, d-, f, and p-. The word "block" was first used to describe this by Charles Janet.
Blocks.
p-block.
The p-block is on the right side of the periodic table. Elements from groups 13-18 are in the p-block.
d-block.
The d-block is in the middle of the periodic table. Elements from groups 3 to 12 are in the d-block.
f-block.
The f-block is shown in green in the illustration above. The elements 57 to 71 are called Lanthanides, elements 89 to 103 are called Actinides. 
s-block.
The s-block is on the left side of the periodic table. Elements from groups 1-2 are in the s-block.