Required Slot

A slot that contains values that are necessary for Alexa to complete the user's request. For example, Alexa, ask Astrology Daily for the horoscope for Taurus. Without the name of the specific zodiac sign, Astrology Daily cannot provide a horoscope. If the user does not provide a value for a required slot, you must ask the user for that slot value. (Source: Alexa Glossary)