A macrodose of psychedelics tends to result in drastic perceptual, cognitive, and emotional changes. This is often referred to as a psychedelic trip, or a journey.
A macrodose could be anywhere between a threshold dose (the dose at which perceptual changes become noticeable, often known as a museum dose, to a heroic dose (where effects like ego death are possible).
On the contrary, a microdose is a small, sub-perceptual dose, which is a tenth to a twentieth of a normal recreational dose of a psychedelics. Microdoses are subtle, and provide ongoing benefits.
Most people microdose psilocybin mushrooms, which are naturally occurring and non-toxic.