Zombie projects are projects that have been ongoing for an extremely extended period of time. It could be because you keep adding tasks to it and the scope expands, or you don't feel like the project's results are what you expected.
Any project that never ends is a "zombie project." This usually happens when:
Our recommendation is that you always stick to the deadlines you set for a project. If you set a goal of finishing a project for a month, you should hand it in it at the end of that month. Also, try to be as specific as you can about what kind of tasks are related to the project, and open up other projects wherever necessary.
If you have any unfinished tasks or if the results are not to your liking after submitting them, you can always start a new one that is more specific to what needs to be done, and / or refer it as "v2" if you choose.
Whenever embarking on a new project, always consider what you will do differently to do your best to meet your defined key results by the end of the allotted time.