What does the term SI units refer to?

The term SI units refers to the International System of Units, which is a globally recognized system for standardizing measurements. This system indeed is organized in multiples of ten, known as the decimal system, which allows for easy conversion between units through the use of prefixes like kilo-, centi-, and milli-. This structure makes it straightforward to scale measurements up or down, facilitating scientific communication and calculations.

The other options do not align with the definition of SI units. For instance, the organization by alphabetical order would not provide a logical structure for measurements. Similarly, SI units are distinct from Imperial measurements, which utilize a completely different set of units such as inches and pounds. Lastly, SI units heavily rely on prefixes to denote different scales of measurement, making the idea of a system without prefixes inaccurate. Thus, the choice that identifies SI units as a system organized in multiples of ten correctly captures the essence of its purpose and functionality.