What is the collective term for the crystalline regions in a metal?

The collective term for the crystalline regions in a metal is often referred to as "Grain." Grains are distinct crystal structures within the metal that are formed during the solidification process and can vary in size, shape, and orientation. The characteristics of these grains affect the overall properties of the metal, such as strength, ductility, and hardness. The boundaries where these grains meet can significantly influence how a metal responds under stress, and manipulating the size and arrangement of grains through processes like annealing can enhance specific properties.

The other terms provided do not appropriately describe these crystalline regions in metals. "Cubic Structure" refers specifically to a type of crystal lattice (like face-centered cubic or body-centered cubic), rather than encompassing all crystalline regions. "Atomic Arrangement" is a broader term that may apply to both crystalline and non-crystalline structures, lacking the specificity needed for grains in metals. "Molecular Grid" suggests a molecular structure associated with compounds or polymers rather than the crystalline structure of metals. Thus, the term "Grain" accurately identifies the critical feature of metal's crystalline regions.