Currently there is no one universally agreed upon definition of 'sensory modulation'....  

A group of occupational therapists researching for a succinct definition came up with this in 2019:

"Sensory modulation is considered a twofold process. It originates in the central nervous system as the neurological ability to regulate and process sensory stimuli; this subsequently offers the individual an opportunity to respond behaviourally to the stimulus".
Anahita Brown, Tamara Tse & Tracy Fortune (2019) Defining sensory modulation: A review of the concept and a contemporary definition for application by occupational therapists, Scandinavian Journal of Occupational Therapy, 26:7, 515-523, DOI: 10.1080/11038128.2018.1509370


How I use the term:

"Sensory modulation is a therapeutic intervention that engages a person's senses to change how they feel" 
Julie O'Sullivan and Carolyn Fitzgibbon (2018) Sensory Modulation, Changing how you feel through Using Your Senses, Resource Manual, Part 1, Ch1:Introduction, p5

I will work with you to discover your unique sensory preferences and challenges, then help develop a range of sensory strategies to incorporate into your life, aiming to assist you to follow your valued directions in everyday life.