Thread:Support/About Wikia:Scavengerhunt-form-error-article-spriteInProgressBarNotFound-sprite-empty/sv/reply

This message references a portion of the sprite (a set of small images combined into one big image for easier loading and caching in browser) that represents an image/icon for a not-yet-found item of the current hunt.

In short, it's what's displayed in the progress bar as a default, not-activated state. I hope that's clearer. :)