What does Comedogenic mean?

For those of you with Adult Acne, this is real information you don't want to miss!

I’m sure you’ve seen this term before.  
Let's break it down;  
comedo = an impaction of varying size containing a mixture of sebum (fancy name for our skin’s oil) and dead skin cells, often known as a “blackhead”;  
genic = creating.  

The scientific term for “blackhead” is Comedo (many, like me, say Comedone).  The start of every acne pimple is a microscopic blackhead, known as a Microcomedone, which is actually in many of our pores, but doesn’t always develop enough to lead to a full blown zit.  A comedogenic ingredient makes the process so much worse, it can aggravate an acne condition, or even start one.

What does "Comedogenic" mean?