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.
An addend is a number on the left hand side of an Addition Math sentence or equation. In this example: 21 + 52 = 73, the addends are 21 and 52. The sum must always bigger than either addend.This fact is useful for helping the student do a quick check on whether his answer is correct.