Note on the origin of various somatic terms.
Titration is a term drawn from chemistry that seems most typically associated, in the somatics trauma literature, with the work of Peter Levine and Somatic Experiencing, though this term is certainly utilized across multiple modalities, including in particular Sensorimotor Psychotherapy. This therapeutic intervention can be understood as a response and reaction to the "flooding" techniques of Prolonged Exposure, which drew concern from multiple practitioners who adopted the Prolonged Exposure technique. Unlike flooding -- which typically refers to the prolonged exposure of a person to an activating circumstance -- titration refers to the delicate mediated "micro-dosing" of nervous system activation to a level where it can be productively metabolized back to safety. The concept of titration has become part of the trauma vernacular and can be found in multiple treatment forms, e.g., Sensorimotor Psychtherapy, "titrated exposure" (Integrative Treatment of Complex Trauma - a CBT-identified methodology), "pacing" in EMDR, etc.
These are all very important terms within the trauma literature, and once again they all refer to very similar processes. These terms all refer to this process of shuttling back and forth between activation and resourcing, i.e., between what is activating and unsafe and what feels calming and safe. Sensorimotor psychotherapy (Pat Ogden) calls this process of moving back and forth between saftey and activation "oscillation," whereas somatic experiencing (Peter Levine) calls it "pendulation." Both of these terms are each also usefully understood as variations on Babette Rothschild's notion of "dual awareness," which again emphasizes the process of helping shuttle a person back to safety when they are in a place of activation. The term pendulation appears to be most commonly utilized and most easily grasped by new clinicians, perhaps because we have such clear visual representations of what a pendulum looks like as it swings back and forth.
Window of tolerance is another term that has become part of the vernacular in somatic psychology. It refers to the domain of activation wherein a client can be productively given a corrective experience by moving them back and forth, within the window of tolerance, from activation to safety. This phrase appears to have originally been introduced into the literature by Daniel Siegel, MD. It bears significant similarities to Kohut's concept of "optimal frustration" -- the zone of developmental challenge that a child will move through as they move through the rupture-repair cycle in relation to a "good enough mother" (Winnicott).
The work of polyvagal theory comes from Stephen Porges, PhD. It refers to the notion that there are evolutionary branches of the vagal nerve that are critical in understanding our trauma response -- particularly our tendency to "freeze with immobilization". Polyvagal theory posits that the "freeze-response" is an evolutionarily primitive, but sometimes appropriate and adaptive response to trauma.