Trika, often called Kashmir Śaivism, is the nondual tantric tradition that flourished in Kashmir from the ninth to the twelfth centuries, culminating in Abhinavagupta. It teaches that Śiva, pure consciousness, freely manifests the universe through his power and conceals and reveals himself, and that liberation is the recognition of one’s identity with him.
Trika
The “triad”: the nondual Śaivism of Kashmir, taught by Abhinavagupta and others.
Also: Kashmir Shaivism