A macrodose is a higher dose of a psychedelic taken to produce full, noticeable effects, in contrast to microdosing, which aims for sub-perceptual effects.
People often describe macrodosing experiences in levels: Level 1 mild shifts in mood and sensory depth; Level 2 brighter colors, slight visual movement, simple closed-eye patterns; Level 3 clear visual distortions and time dilation; Level 4 strong visuals with boundaries blending and a reduced sense of self; Level 5 complete immersion with little connection to ordinary reality.
Experiences vary widely by person, substance, and context, and legality differs by location. For background on psilocybin and its effects, see this overview: psilocybin.
I hope this clarifies the term.