On the subject of foam rolling, the term "trigger point" may have been brought up when talking about myofascial release. I found two links that do a good job on explaining about trigger points. Check out the TriggerPoint's SITE and Youtube video below. I also highly recommend Trigger Point Therapy's products. I have been using their products with my clients, peers, and myself for 5+ years.
The video below includes a visual and audio explanation of what trigger points are.
Next week, we will start linking and creating content on how to perform some mobility exercises to ameliorate those nasty knots/trigger points in your muslces.