Here's a breakdown of the meaning:
* Ketiva (כתבה) refers to the inscription of our deeds in the Book of Life during Rosh Hashanah.
* Chatima (חתימה) refers to the sealing of those deeds on Yom Kippur.
* Tovah (טובה) means "good."
The phrase is a blessing wishing for a favorable judgment and a good year ahead. It's often said to others during the High Holidays as a way to express hope for a positive inscription of their deeds and a successful year.