milestone is a point were we can check our process 
achivements steps and if are not in proper way throu we 
must here come readjusting goal. every team always go to 
this process planing->devlopment->testing in time sedule. 
if it not happen goto Readjustig goal same work in diffrent 
way

Depending on the situation adjust it

Milestone: Date by which major activities are performed.
Readjusting: If the milestone seems not to be achieved as
targeted or incur a risk, it should be readjusted setting
goals with different approach.

In addition to above mentioned points, During Project 
development process, whenever there is a requirement 
change / requirement correction happens. PM will need to re-
adjust the goal and milestone.

The recognition of an important event within the project,
usually the achievement of a key project deliverable