Is magic explained anywhere in any official 5e books?

Like: What's the difference between arcane and divine? What are spell slots exactly?

— Lio Leeuwerink (@UndertakerSheep) September 13, 2017

Curious about magic in D&D? See part 3 of the PH, "The Rules of Magic." Spell slots, arcane magic, divine magic—it's all discussed. #DnD https://t.co/VEfIbRT1EH

— Jeremy Crawford (@JeremyECrawford) September 13, 2017

Thanks for the reply. I can’t find any mention of what a spell slot IS within the game’s lore tho. It’s only discussed as a mechanic 1/2I know how spellcasting works. I'm curious what a slot is lore wise, since it's quantifiable. Is it like mana? Partitioned parts of a mind?

— Lio Leeuwerink (@UndertakerSheep) September 13, 2017

In the "Spell Slots" section, see the sentence that starts, "Manipulating the fabric of magic and channeling its energy …"

— Jeremy Crawford (@JeremyECrawford) September 13, 2017