وَلَهُ صِيغَةٌ وَاحِدَةٌ، وَهِيَ الْمُضَارِعُ مَعَ «لَا» النَّاهِيَةِ
It has one basic form: a present-tense verb with prohibitive lā.
لَا تَخْرُجْ
Do not go out.
Lā al-nāhiyah is a prohibitive and jussive particle. It places the following imperfect verb in the jussive mood. In this example, the final sukūn on “takhruj” marks that mood.
Calling the expression a “prohibitive form” describes its grammar. Identifying its actual rhetorical force in a particular context is a further step.