Broadly, projections refer to statistical predictions made by experts. In season-long fantasy basketball leagues, projections are often released in the months leading up to the season as a means of providing a guide for fantasy players. They're typically rooted in a combination of past production and expected future output.
Projections can vary in scale and are also used in daily fantasy basketball. In this case, the goal is to project a player or team's output for just one game, as opposed to an entire season.