What is Progressive Aspect

PROGRESSIVE TENSES

i. Present progressive
= am  + (base form + -ing) :  I am working.  OR is + (base form + -ing)         e.g: She is eating. OR  are + (base form + -ing) 
e.g:  We are studying.

a. A planned activity.
   Sofia is starting school at CEC tomorrow

b. An activity that is occurring right now.

            Jan is watching TV right now.

c. An activity that is in progress, although not actually occurring at the time of speaking.

            Sara is learning English at CEC.

ii. Past progressive
 = was  + (base form + -ing) : I was working.  OR were + (base form + -         ing) 
  e.g: They were eating.

a. A past activity in progress while  another activity        occurred.

            At 6:00 yesterday I was eating dinner.

            The phone rang while I was eating.

b. Two past activities in progress at the same time.

     While I was answering the phone, my wife was     
     cooking dinner.

ii. Future progressive
 = will be + (base form + -ing): I will be working. 
e.g : He will be eating.

 An activity that will be in progress.

  a. Tomorrow Sam will be studying for the test on Unit 1.

sources:

http://en.wikipedia.org/wiki/Continuous_and_progressive_aspects

http://www.grammar-monster.com/glossary/progressive_aspect.htm