Freak can mean several different things:

1. Something highly unusual or unexpected, especially when it seems to happen by chance. A freak accident is one that occurs in a bizarre, unpredictable way. A freak storm appears suddenly when the weather forecast predicted sunshine. Athletes sometimes achieve victories through freak plays that nobody could have planned. The word suggests something so unusual that it seems almost impossible.
2. To become very upset, anxious, or lose your composure. When someone freaks out, they might start yelling, panicking, or acting irrationally. A student might freak out before a big presentation, or a parent might freak out when they can't find their child in a crowded store. The phrase don't freak out means “stay calm” or “keep your cool.”
3. Someone intensely enthusiastic about something. A health freak cares deeply about exercise and nutrition. A neat freak keeps everything perfectly organized. While this usage can sound negative, it can also just mean someone is passionate about their interest.

The word carries different feelings depending on context. Freak accidents can be frightening because they're unpredictable. Someone freaking out has lost control of their emotions. But calling yourself a baseball freak just means you really, really love baseball.