Pi'el

In Hebrew, verbs, which take the form of derived stems, are conjugated to reflect their tense and mood, as well as to agree with their subjects in gender, number, and person. Each verb has an inherent voice, though a verb in one voice typically has counterparts in other voices. This article deals mostly with Modern Hebrew, but to some extent, the information shown here applies to Biblical Hebrew as well.

Verbs in Hebrew, like nouns, adjectives, and adverbs are formed and declined by altering a (usually) three letter root. However, the root can be identified as having a different pattern than normal in certain cases.

A root that contains at least one of the "weak" letters א‎ alef, ה‎ hey, ח‎ het, י‎ yod, נ‎ nun, ו‎ vav, and ע‎ 'ayin or two of the same consonant is called a weak root. Each pairing of a weak letter with a position results in a slightly different conjugation pattern. Resh ר is often considered a weak letter, though it occasionally functions as a strong letter, depending on speaker and era of the language. Roots without weak letters are called strong roots, among other names.

...
Wikipedia