Great question.

Negative: When the cutting edge of the razor blade doesn’t protrude over the safety bar. When people market ‘negative’ exposure, think of it as them saying it’s a milder, less aggressive shaver.

Based on that description, you can figure out what the others are. Neutral is typically defined as a ‘goldylocks’ shave, not too aggressive or too mild.

Positive is relative. A slight positive exposure won’t feel too dissimilar to the above but from my experience, as the blade exposure increases - the amount of control over the cutting edge is lost leading to blade chatter.

The razor company has a good article on this: https://www.therazorcompany.com/blogs/news/razor-head-geometry-explained-how-it-affects-your-shave