General Idea
Concept, Notion
An approximation of thought is just thinking up the general idea. The concept or notion.
がいねん
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
ほとんどの無神論者は、神や神々の概念に対して否定的です。
Most of the atheists have negative feelings regarding the concept of God or gods.