Mnemonics are a technique to help you remember something easier. Technically speaking, any technique you use to help you remember something can be a mnemonic. We often see in movies when doctoral students, who are ungodly brilliant, of course, will memorize long complex acronyms and suddenly ace their exam.
When they come up with these acronyms, like say, HMOG HWIP FMTTY, the brain is able to use these devices to remember that that phrase, in fact, means “Holy Mother of God, How Will I Pay For My Tuition This Year?”
Especially when shouted from the rooftops, praying someone will listen.