"Grammar lessons" refers to learning and understanding the rules and structure of a language, which helps in using the language correctly while speaking or writing. Full definition
Remember the middle school grammar lessons you slept through? (jeffbullas.com)
While you probably studied the grammar, it's likely that their English skills are derived much more from grammar lessons than yours. (sbnation.com)
For this reason, this lesson is a straight forward, teacher - centered, grammar lesson focusing on written and oral production of the target structure. (thoughtco.com)