Credit recovery in my state means that after a high school student has failed a class that he or she needs to graduate, he uses credit recovery to retake the class in condensed time. From what I've observed in my district and from talking to other teachers in various states, credit recovery is an online program. I have never heard of normal face-to-face classes such as summer school being called credit recovery.
Our school district bought the rights to a credit recovery program which students can use after school or during the summer. They have to be in a designated lab with a "proctor" who ensures that they are the ones completing the course online. Students generally can move as quickly as they want through a course; so many see credit recovery as being advantageous over regular classes.
I will say this, though, about credit recovery. Normally, when a student fails a class, that permanently affects his GPA and record. So, credit recovery allows a student to get the credit hours he needs for graduation but does not eliminate the negative marks on his record. Moreover, in my state, students must pay for credit recovery, and it can get expensive if someone fails more than one class (one that was free to the student when he took it the first time!). Finally, some of my students have complained that credit recovery is boring and that they don't understand a lot of what they are supposed to be learning online. The proctor in the lab with them is normally there to answer technology questions and to try to prevent cheating, but he or she cannot answer questions about all the subjects that students are studying.
Credit recovery refers to what you do after you have failed a class or some classes in high school. High schools across the nation typically have some required number of credits that you have to have in order to graduate. Some of these are elective credits and some must come from taking specific credits.
If you fail a required course, or if you are getting to the point where you're in danger of not having enough credits to graduate, you need to do credit recovery. This can typically be done in summer school or, nowadays, online.