What is a four sided figure characterized by having no parallel sides and unequal adjacent sides?

The four-sided figure characterized by having no parallel sides and unequal adjacent sides is referred to as a trapezium in some regions, especially in British English. This term describes a quadrilateral that does not meet the criteria for other more regular shapes like rectangles, rhombuses, or trapezoids (which often have one pair of parallel sides).

In the context of geometry, the trapezium's defining features highlight its irregularity. The absence of parallel sides means that the angles and lengths can vary widely, contributing to its classification as an irregular quadrilateral. Recognizing this shape is crucial for applications in various fields such as engineering, architecture, and design, where understanding geometric properties can impact structural integrity and aesthetic decisions. The clarity of distinguishing between trapezium and trapezoid is important since the terminology can differ based on regional definitions, yet in this case, identifying the unique attributes of a trapezium confirms its correctness as the answer.