Chief of Science
On the bridge, the science position is responsible for analysis of sensor scans. Generally the scans themselves are run by the Operations officer, but the analysis of the scans - getting into the gritty, detailed scientific facts obtained by the scans- is the job of the science officer.
On an away mission, the science officer is responsible for data gathering and analysis. The science officer reports the findings to the Away Team commander as well as records their findings for later detailed analysis aboard the ship.
In the labs, the science department conducts experiments and creates reports of scientific analysis of data. Each science officer generally has an area of expertise and they work in that particular area.