A Stand is a familiar or a apparition coming from ones spiritual energy. Stands have unique abilities and come in many different types and styles. Some are meant for battle others are not. Some are meant for close range which are the most powerful and others meant for long range and are generally the weaker ones. Others can come as guns or swords and even animals can develop stands if their spiritual energy is strong enough.
There are downsides to having a Stand. Since they are tethered to you whatever damage is inflected upon them is inflicted upon you as well I.E. stand gets cut on their hands you get cuts on your hands. Another downside is if your spiritual energy is not powerful enough to control your Stand you're in danger of the stand taking control and killing you.
For more information (Stats rubric, Trivia, Need a better explanation because i'm bad at explaining things, etc) or a list of types and examples refer to these.
Information about Stands
Stand Types Lists
So what would your Stand and its ability be?
Soul wrote: Here's a neat something I came across. It generates a Stand power, complete with a description and rankings, given a band/song name, since JoJo has a myriad of musical references. http://www.pages.drexel.edu/~dft29/Stan ... drive.html