Enceladus' ice plumes might be the reason why a dark spot on the moon is disappearing. But what is the spot in the first place?

There's a weird, disappearing dark spot on Saturn's moon Enceladus

Source: space
Source Link: https://www.space.com/space-exploration/search-for-life/theres-a-weird-disappearing-dark-spot-on-saturns-moon-enceladus