1. Without advance preparation
   - ad lib, spontaneously, impromptu

Encyclopedia: Ad libitum

• form class
• form division
• form family
• form genus
• form genus Rhizoctinia
• form letter
• form of address
• form of government
• form-only
• formal
• formal garden
• formal logic
• formal semantics
• formaldehyde
• formalin
• formalisation
• formalise
• formalised
• formalism
• formalist
• formalistic
• formalities
• formality
• formalization
• formalize