Is it a grouping of spirits or just one single spirit?
A couple of years ago I wrote a post on visual snow called, Seeing Static? The Spiritual Meaning Behind Visual Snow, and while this topic has recently come up again.
People want to know if it is one spirit visiting you or if more than one, and the answer is that it can be both. You just have to separate the energy and ask for them (the spirits) to stand in separate places to get a good identification on them. I talk about how to do this more in my Spirit Identification Key eBook, and I also talk about how to discern if what you are picking up is residual or an actual spirit.
In the early days of mediumship, visual snow and any physical mass that semi-materialized in the presence of spirits or in the creation of spirits was called ectoplasm, a term coined from the Greek word ektos meaning outside and something formed and molded (source: Wikipedia).
If you're saying wow that sounds very familiar to what I've heard in the movie Ghostbusters, it can't be a real word - it is.
Dan Aykroyd's father, Peter, was a spiritualist historian who wrote the book The History of Ghosts on the topic, and this work heavily influenced the inclusions and topics addressed in that movie, understandably, it was his father's and his grandfather's work. If you'd like to learn more about this topic, I highly suggest Colin Dickey's article on it here.
If you are seeing visual snow a lot, or that static-y like air and it's just recently been after the passing of a friend or family member... this is a sign you're clairvoyant and that these spirits are attempting to visit you.
If neither has happened and you're seeing these things... it could be a sign that clairvoyant abilities are coming in or that your spirit guides want to contact you.
Either way, visual snow is technically a physical spirit manifestation that used to be a popular spirit trick back in the hey-day of the mediumship era around the 1850s and through the early 1900s.
Now most spirits communicate through voice and sound, technically a mental spirit manifestation, as this is the more preferred method of mediums of recent years - but that doesn't mean that some spirits won't go back to the original way.
Seeing a lot of visual snow around you is for the clairvoyant what hearing ringing in the ears is for a clairaudient. It's a sign you're piercing the veil and tapping into the spirit world. Which can happen either intentionally or accidentally, depending on how you want to look at it.