A science project is an academic assignment in which students perform an experiment or create a model.
In 2364, Wesley Crusher did a science project that involved a model of the tractor beam used by the USS Enterprise-D, but with a few modifications of his own added. (TNG: "The Naked Now")
In 2366, Crusher was working on a project in Advanced Genetics when he accidentally released two nanites on the USS Enterprise-D, leading to malfunctions throughout the ship. (TNG: "Evolution")
In 2368, Captain Jean-Luc Picard took three students with prize-winning science projects on a tour of the USS Enterprise-D which was interrupted by ship-wide disruptions caused by a quantum filament. (TNG: "Disaster")
In 2370, Jake Sisko mentioned to Miles O'Brien that he couldn't figure out how to get the emitter crystal on his science project, a subspace transceiver model to work. When O'Brien agreed to help him, Jake asked if it might be a conflict of interest to have his teacher's husband help him on the project, but O'Brien didn't seem to think so, as long as she was made aware of the fact beforehand. (DS9: "Whispers")
Later that year, Jake and Nog were assigned a science project by Keiko. They traveled to the Gamma Quadrant to perform a planetary survey with Benjamin Sisko but ended up encountering a group of Jem'Hadar and Eris, a Vorta. (DS9: "The Jem'Hadar")
In 2376, all the children aboard the USS Voyager took part in the Annual Voyager Science Fair, in which each student presented a science project. (VOY: "Child's Play")