Suppression refers to a phenomenon whereby someone is consciously trying to forget or let go of a particular memory. This is usually related to traumatic and bad memories that have negative or painful effects on someone. For example, a lady being raped, when asked after some years, will most likely tell you she has never been raped. That is simply because she is trying to suppress that memory. On the other hand, repression has to do with a situation whereby a person unconsciously forgets his or her feelings.
This is actually due to the fact that he was not fully aware of that memory. For example, nobody can remember when he or she started to walk or crawl. Therefore, there will surely be repression in memory. These terms "repression" and "suppression" are usually used in psychology. They are defense mechanisms used by people when an incident occurs, just to forget or stay away from an unwanted memory.