Why star symbol appeared in android phones?

Many of us use android phones and some cases we could have noticed star symbol will be appeared in top as like below.

    This symbol indicates that priority calling is set and when ever call comes we will not get the ring sound. This is similar to silent profile. This can be enabled/disabled as like below in Motorola mobiles. Click on the volume button to increase/decrease. Now click on priority and we can see star appearing in the top and if we wanted to remove select in All instead of priority.