Act of immuring or enclosing.
(1) A method of burial by which bodies are enclosed in oven-like chambers constructed of solid masonry.
It is sometimes used in places where the soil is such that ordinary burial is impracticable, e.g., Mexico City.
Upon clearance of these chambers, bodies are sometimes found mummified.
These have upon occasion been sold and exhibited as "walled-up nuns," or "victims of the Inquisition."
(2) Voluntary permanent closing-up of the door of the cell of a religious, who continued to receive food, light, and air through a window, and followed the ceremonies of the Church through an opening or "squint" in the chapel wall.
Rider Haggard exploited and exaggerated the practise in one of his novels; Enid Dinnis has written charmingly of it in "The Anchorhold."
New Catholic Dictionary