I made him understand the situation. Here ‘understand’ is a-

In grammar, the infinitive form of a verb without the word “to” is called ‘Bare infinitive’ or the base form of the verb.
In the sentence, “I let him go” the bare infinitive is the word ‘go’.

আলোচ্য বাক্যে ‘understand’ Bare infinitive হিসেবে ব্যবহৃত হয়েছে

Source: Cambridge Dictionary