What does "insider" mean?

A person who has special knowledge about the inner workings of a group, organization, or institution.

Insider

Common synonyms include: affiliate, associate, belonger, brother, business connection, card carrier.

/ɪnˈsaɪdɚ/ noun

noun ·Uncommon ·Advanced level

Noun

1
A person who has special knowledge about the inner workings of a group, organization, or institution.
"Near-synonyms: initiate, old hand, habitué"
2
an officer of a corporation or others who have access to private information about the corporation's operations wordnet
3
A person who is within an enclosed space.
"To the insider, the ceiling is like a small firmament twinkling with astral radiations."

"The insider trading scandal put a lot of people out of business."

From inside + -er.