Full Idea
Many later Buddhists (after Nagarjuna, c.120 CE) developed a belief that everything we experience is an illusion: in the West we would call them idealists.
Gist of Idea
Nagarjuna and others pronounced the world of experience to be an illusion
Source
report of Nagarjuna (teachings [c.120]) by Karen Armstrong - A History of God Ch.3
Book Reference
Armstrong,Karen: 'A History of God' [Mandarin 1993], p.101
A Reaction
This is just one step beyond Plato (who at least hung onto the immediate world as an inferior reality), and is presumably intended to motivate meditators to break out of the misery of existence into a higher realm. Personally I am against it.