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.
Pre-exposure prophylaxis. Pre-exposure prophylaxis (PrEP) is the preemptive use of drugs to prevent disease in people who have not yet been exposed to the disease-causing agent. In particular, the term is used to refer to the use of antiviral drugs that attack the lifecycle of the HIV virus as a strategy for the prevention of HIV/AIDS.