var := x;

x = 10; var

x = 20; var

Module[{x}, x = 50; {x, var}]

x

Module[{x}, {x, var}]

Block[{x}, x = 80; {x, var}]

x

Block[{x}, {x, var}]

SumBlock[x_]  :=  Block[{i},  Sum[x^i,  {i,  1,  4}]] SumModule[x_]  :=  Module[{i},  Sum[x^i,  {i,  1,  4}]]

{SumModule[a], SumModule[i]}

{SumBlock[a], SumBlock[i]}