The phrase "prolific season" means a period of time in which there is a tremendous amount of production, success, or achievement in a particular field or activity. Full definition
The winger has thrived under the tutelage of Pep Guardiola at Manchester City and, with 20 goals in all competitions, it's been his most prolific season in front of goal by some distance. (footballwhispers.com)
Raheem Sterling scored a vital third and is enjoying his most prolific season in the Premier League. (caughtoffside.com)
Alex Sandro has three, equalling his most prolific season for the club set last year. (uefa.com)