Primarily a philosophical term referring to the doctrine that true knowledge is unattainable, or a general skeptical attitude.
From a skeptical standpoint, he argued that absolute truth does not exist.
We learned about skepticism in philosophy class.
From 懐疑 (かいぎ, 'doubt') + 論 (ろん, 'theory'). The exact historical derivation is uncertain, but the term is a standard Sino-Japanese compound for philosophical skepticism.