In this paper, we attempt to summarize online discussions by filtering posts. Selecting the highly related posts from the discussion boards leads to a summarized version of the discussion. Online discussion summarizer (ODS) is based on unsupervised information retrieval techniques. Four features are used in the summarization function; which are the term frequency inverse post frequency, title term frequency, description term frequency and author reputation. This paper shows that combining the four features in the same function results in higher accuracy than using each alone. ODS was able to summarize online discussions with an accuracy of 72%, precession of 83% and recall of 62%.