Refers to the half of the basketball court where the team with possession of the ball attempts to score. Ncaabasketball.com defines a team's frontcourt as "the part between the division line and its own (basket) end line". (This definition is also valid for the NBA).
The offensive team's frontcourt is the same as the defending team's backcourt.
The frontcourt is also a term used to collectively describe a team's small forward, power forward, and center (usually the 3 tallest players on the team, who play closer to the basket than the smaller guards).
While there's many opinions on the greatest frontcourt of all-time, the 1980s Boston Celtics trio of Larry Bird, Kevin McHale, and Robert Parish is at or near the top of most lists (including mine).