What do you mean by "movement along a demand curve?"

When quantity demanded of a commodity changes due to a change in its price, keeping other factors constant, it is known as change in quantity demanded. It is graphically expressed as a movement along the same demand curve. There can be either a downward movement or an upward movement (Contraction in demand) along the same demand curve. 
Let us understand the movement along the demand curve with the help of Fig:

 

  Figure: Movement along Demand Curve.