To summarize means to sum up the main points of something — a summarization is this kind of summing up. Book reports are big on summarization: it makes you practice reading and synthesizing the book and proves you read it.
When you're a trial lawyer, the last part of the argument you make before the court is called a summation. It included a summarization of the points you have made in the trial so far, but it goes one step further, to push this summarization toward a conclusion you hope the judge or jury will accept.
