The Five Verbs (الأفعال الخمسة) — also called the الأمثلة الخمسة — are not five specific verbs, but rather five conjugation forms of the present tense (المضارع) that share a special إعراب pattern. They are the forms that have an appended alif or waw representing the subject: يفعلانِ, تفعلانِ, يفعلونَ, تفعلونَ, and تفعلينَ.
What makes these forms special is how they show grammatical mood. In the indicative (مرفوع), they retain the نون (noon) at the end: يكتبانِ (they two write), يكتبونَ (they write). In the subjunctive (منصوب) and jussive (مجزوم), the نون is dropped: لن يكتبا (they two will not write), لم يكتبوا (they did not write).
The sign of رفع for the five verbs is ثبوت النون (the presence of the noon), and the sign of both نصب and جزم is حذف النون (the removal of the noon). This is another example of إعراب not through vowel marks but through the presence or absence of a letter — similar in principle to the Five Nouns and the sound masculine plural.
Recognizing the five verbs is crucial for correctly parsing Arabic sentences, especially when they follow particles like لن (will not — causes نصب) or لم (did not — causes جزم). The Nahw courses on Ilm Al Lughah provide extensive drills on identifying and parsing these forms, with flashcards that test your ability to apply the correct mood in various contexts.