A team's scoring efficiency is measured by dividing the number of scores by the number of scoring opportunities they had. A scoring opportunity is up to interpretation, but typically references the red zone for touchdowns, and in front of the 50-yard line for field goals. The red zone is the area on the field between the opponent's 20-yard line and the end zone.
A team's scoring efficiency needs to be in the upper echelon of the league in order to be considered a good team. A team with a low scoring efficiency rating frequently misses on scoring opportunities. A team like this would be considered "weak" in the red zone. Scoring efficiency most often refers to touchdowns, but can also be used to measure a team's ability to score field goals. If a team attempts a field goal and misses, that counts against their scoring efficiency.