Question

What is meant by cave and stack

Answer 1

stack or sea stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion.

cave is a hollow place in the ground,[1][2] specifically a natural space large enough for a human to enter. Caves form naturally by the weathering of rock and often extend deep underground.

Answer 2

Cave is a natural underground chamber in a hillside or cliff.

Stack is a pile of objects, typically one that is neatly arranged.
or
Stack is a chimney, especially one on a factory, or a vertical exhaust pipe on a vehicle.

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