Borrowing its name both from ancient alchemical practices – like the famed transmutation of lead into pure gold – and physics – wherein transmutation means the changing of one element into another by radioactive decay, nuclear bombardment, or something else equally scientific and/or likely to give you unwanted side effects.
Transmutation magic, therefore, deals with turning one thing (or person) into another. It’s easily the school of magic that most closely resembles science in our own world, although this burning curiosity can give way to a sense of burgeoning godhood in the more powerful wielders of Transmutation magic.
One who has mastered Transmutation commands the raw energy of creation, crafting both physical forms and mental qualities as you see fit – a smith who forges reality itself rather than base metals.
Transmutation's ties to the natural world also makes this school the preferred type of magic practiced by Druids and those with ties to the natural world – although it’s unlikely you’d ever find a druid who knows (or cares) that their Druidcraft is a Transmutation Cantrip.