A verb form (the causative form) that expresses causing or letting someone do something (e.g. 'to make/let someone eat' or 'to have someone go').
「子供に野菜を食べさせる」の「食べさせる」は使役形です。
'The "tabesasero" in "to make a child eat vegetables" is the causative form (使役形).
日本語の初級文法では、使役形を『〜させる／〜せる』として学びます。
In beginner Japanese grammar you learn the causative form as '~saseru/~seru.'
彼は部下に報告を書かせた――この文は使役形の使用例です。
He made his subordinate write a report — this sentence is an example of the causative form.