Cross-laminated timber (CLT) is a wood panel product made from gluing together layers of solid-sawn lumber, i.e., lumber cut from a single log. Each layer of boards is usually oriented perpendicular to adjacent layers and glued on the wide faces of each board, usually in a symmetric way so that the outer layers have the same orientation.
An odd number of layers is most common, but there are configurations with even numbers as well (which are then arranged to give a symmetric configuration).
Regular timber is an anisotropic material, meaning that the physical properties change depending on the direction at which the force is applied. By gluing layers of wood at right angles, the panel can achieve better structural rigidity in both directions.
It is like plywood but with distinctively thicker laminations or lamellae.