What does "columnar" mean?

Columnar: Formed in columns; having the form of a column or columns; like the shaft of a column. Columnar epithelium (Anat.), epithelium in which the cells are priismatic in form, and set upright on the surface they cover. -- Columnar structure (Geol.), a structure consisting of more or less regular columns, usually six-sided, but sometimes with eight or more sides. The columns are often fractured transversely, with a cup joint, showing a concave surface above. This structure is characteristic of certain igneous rocks, as basalt, and is due to contraction in cooling.