Hertz measures cycles per second - one Hertz is one cycle per second. Unlike gauss that is a measurement unit for the strenght of a specific thing (an electromagnetic field), hertz is a generic frequency measurement.
Prepend is a word that means to attach content as a prefix. It is often used in different kinds of programming and in automated processes. Some prepending is done manually as a user. For example, a prepend command could be used in a scripting language that a programmer would enter into a certain function or code module. It would add certain characters of text to the beginning of some variable or object.
The word 'addend' was first used in the early 1900's and comes from the Latin word 'addendus' which means 'to be added.'. Addends are sometimes referred to as summands, and the first addend in a sequence is also called the augend. Any term can be an addend, it does not have to be a number.