A motion to suppress is a written request to prevent the government/prosecutor from using certain evidence against you in a criminal trial and would be decided by a judge - it is not decided by a jury. For example, the police search your car or your home illegally and find illegal drugs or other evidence of a crime (ie. the bloody knife). A motion to suppress would be filed by your attorney to prevent the government from using the drugs and/or the knife against you at trial. Often times, this results in your case being dropped !