A ṣīghah is a particular form in which a word occurs. Words derived from the same root may have different forms, each contributing a grammatical or semantic distinction.
Word / formMeaning / explanation
كَتَبَhe wrote.
كَتَبْتُI wrote.
كَتَبُواthey (masculine) wrote.
The act of writing is shared, but the identity and number of the doer differ. Recognizing a form therefore requires attention to its letters and vowel marks, including its endings.