The listed topics are related to utilities for converting data types and units. See in AutoLISP Function Synopsis (AutoLISP), for a complete list of conversion functions.
About Angular Conversion (AutoLISP)
Angular values returned by most AutoLISP functions and those stored in a drawing are expressed in radians, while angular input is commonly provided in degrees or another angular format than radians.
About Unit Conversion (AutoLISP)
Values that represent distances, volumes, or other forms of measurement can be converted from one real-world unit to another.