What kind of plant tissue is not epidermis or vascular tissue?

It is ground tissue.
Plant's ground tissues are neither a vascular nor a dermal or dermis. Ground tissues can be divided into 3 categories based on the nature of walls' cell. It is Parenchyma - cells having a narrow and fine primary walls and remain alive when it matures, Collenchyma- cells having a narrow and fine primary walls in the other areas of secondary thickening; it gives extra structural and mechanical support specifically in the area wherein new growth happened, lastly is Sclerenchyma - cells having thick woody lignin inside cell walls and may sometimes die when matures; it gives structural support to a plant.

Active site is where they touch.