An insider threat in cybersecurity is when someone from within an organization misuses their access to steal information or harm the organization. It's like a trusted co-worker sharing company secrets with a rival or intentionally causing damage from the inside.
Imagine you work at a company that develops a new secret recipe for a popular soft drink. One of your colleagues, who has access to the recipe, decides to sell it to a rival company for a large sum. This act of sharing sensitive information with a competitor is an example of an insider threat.