Sacred Texts
It said that when Shiva (divine masculine) as a teacher revealed knowledge to Shakti it is known as an Agama. When Shakti (divine feminine) as a teacher revealed knowledge as a teacher to Shiva it is known as a Nigama.
Though Agamas, Nigamas and Tantras are used interchangeably they all have certain defining yet shared traits. Agamas are often practical and outline practices such as how to worship in a Temple. Nigamas refer to the 4 Vedic texts Rig-Veda, Sama-Veda, Yajur-Veda, and Atharva-Veda, and focus on the knowledge of the gods. The Tantras are associated with the techniques or the rituals.