* It's a misspelling. Perhaps it's a variation of a real word, such as "Ishmael" or "Ishtar."
* It's a name. "Ishba" could be a person's name, potentially from a specific culture or language.
* It's a fictional word. It might be part of a made-up language, a story, or a game.
To get a more definitive answer, you'll need more context. For example, where did you encounter the word "Ishba"? Was it in a book, a movie, a conversation?
Knowing the source will help determine its meaning.