It is a very general and informal way of saying that something has occurred, but without specifying what it is. It can be used in a variety of situations, such as:
* When someone tells you about an event:
* "Nanika atta?" - "Did something happen?"
* "Ee, nanika atta." - "Yeah, something happened."
* When you notice something unusual:
* "Nanika atta yo ne?" - "Something happened, right?"
* When you want to know what happened without being specific:
* "Nanika atta?" - "What happened?"
The phrase "nanika" means "something" and "atta" is the past tense of the verb "aru" (to be, to exist).
It's important to note that the exact meaning of "nanika atta" can vary depending on the context and tone of voice used.