In science fiction, it's called the "life force" or just "energy". In Eastern traditions, it's called prana or qi. Some might associate it with the soul or spirit. And many educated people believe it exists in some form as a unique force underlying all life.
Corrollaries are that sickness results in, or from, disruption of the vital force, and that death occurs when it is lost.
I don't believe in vitalism. I have a mechanistic view of life, which means that I see living things as enormously complex machines. That does not mean I don't believe in a spiritual realm, only that I believe there is no scientific basis to support the concept of a "vitalistic force". Every description of it I have read or heard is metaphysical in nature, and therefore not scientific.
I was surprised to see this headline: "M.D. Anderson scientist finds life's essence". Was a vital force discovered right in my backyard when I wasn't looking?
It turns out that to a newspaper science writer, "life's essence" refers to the mechanism of cell division, not to "life force". So the vitalists are back to square one.
Or are they? When I first heard of "biophotons", I thought they were just another pseudoscientific quack theory invented to sell a new line of products. It turns out they are real, having been described in, for example, the journals Modern Physics Letters B and Cell Biophysics long ago. The details are well over my head, but they seem to be involved in cell communication. It looks mechanistic to me.
But not all researchers agree it's mechanistic. Apparently, according to this book, there are two conceptions of biophotons: a mechanistic one and a vitalistic one. The vitalistic one is proposed by real scientists.
It has to do with quantum mechanics (or something called "modern quantum optics"). That's it: invincibly over my head. I'm out of the commentariat on the subject due to inability to understand it anymore.
All I can say is, maybe it will turn out there is something to the idea of a vital force after all.