Unintentional means not done on purpose. When something is unintentional, it happens by accident or without someone meaning for it to happen.

If you knock over a glass of milk while reaching for the salt, that's an unintentional spill. You didn't wake up that morning planning to spill milk. Your hand just moved the wrong way, and suddenly there's a puddle on the table. If you step on your friend's foot in the lunch line, that's unintentional: you weren't trying to hurt them, you just didn't see where their foot was.

The word is especially important when thinking about fairness and consequences. When a teacher asks whether you broke a rule unintentionally, she's trying to understand if you made an honest mistake or chose to disobey. When referees judge whether a foul in basketball was intentional or unintentional, they're deciding if a player meant to break the rules or just got tangled up during fast action.

Unintentional mistakes still have consequences (you still need to clean up that milk), but people usually respond with more understanding when they know you didn't mean to cause the problem. The opposite is intentional or deliberate, meaning done on purpose with full awareness of what you're doing.