Question

no one expected an incident like this to happen. this event has changed everything. what does incident mean?

Explanation:

Based on the context of an unexpected event at an amusement park that changed everything, "incident" refers to an unplanned, usually negative or notable event or occurrence.

Answer:

An unplanned, notable (often negative) event or occurrence; in this context, it refers to the unexpected, impactful event at the amusement park.