What term is used to describe solid forms characterized by the absence of long-range order?

The term that describes solid forms characterized by the absence of long-range order is "amorphous solids." These solids do not have a well-defined geometric structure, which means that their molecular arrangement is random and lacks the repeating patterns typically found in crystalline solids. This unique structure leads to different physical properties, such as solubility and stability, compared to crystalline materials.

Amorphous solids are significant in pharmaceutical sciences because they can enhance the solubility and bioavailability of drug compounds. For example, when a drug is in an amorphous form, it may dissolve more readily than in its crystalline form, potentially leading to more effective therapeutic outcomes.

In contrast, crystalline solids feature a highly ordered structure with a repeating unit cell, which is not the case for amorphous solids. Polymeric solids and complex solids refer to different categories of materials and structures, further distinguishing them from the characteristics that define amorphous solids.