An undeveloped cryptocurrency project.
Vaporware refers to the category of cryptocurrency projects that were conceptualized but never developed. In other words, the developers of these projects had an outline and maybe a roadmap for them, but could not implement these projects due to a lack of resources or other factors.
If scores were kept of all the crypto projects that have ever been theorized, vaporware would make up the majority of these projects. Essentially, it is any idea thought up and reasoned to bring about some benefit but never passed this stage. Thus, it is only vapor.