The title alerts us to the 'big idea' or central concept around which the novel orbits. It sounds like something that's somehow beautiful and horrible at the same time, like the novel itself.
Shining or shining on is the phrase used by Dick Halloran to describe his and five-year-old Danny Torrance's ability to read minds and mentally converse with others who read minds. When Halloran talks to Danny privately he tells him:
"You shine on boy, harder than anyone I ever met in my life. […]. You got a knack. […] Me I've always called it shining. That's what my grandmother called it, too. She had it. We used to sit in the kitchen when I was a boy and have long talks without even opening our mouths" (11.7,9).
Halloran and Danny can also see things that happened in the past and things that might happen in the future. Later in the same scene, Halloran explains to Danny:
"What you got, son, I call it shinin on, the bible calls it having visions, and there's scientists that call it precognition. I've read up on it, son. I've studied on it. They all mean seeing the future." (11.78)
This is probably welcome news to Danny because his ability is finally being acknowledged and verified. On the other hand, Danny's been having visions of murder and mayhem at the Overlook, so Halloran's verification is also probably vastly frightening. But, as their further discussion reveals, there's still hope because the visions don't always come true.
What neither Danny nor Halloran seem to understand is the reason that these visions don't always come true. Alice Cullen from the Twilight series might be able to tell them a thing or two, though. She could explain that visions don't always come true because people can change their minds and their plans. People who are given visions of tragic events set to happen in the future might have the power, or even the responsibility, to try to change them.
The visions of the Overlook that Danny begins having when his father, Jack, is up for the caretaker job are definitely warnings – warnings not to go there. He knows it, too. Sadly, he also believes, along with his parents, that the job at the Overlook is Jack's final opportunity to fully recover from his alcoholism and finish his play. It's the final opportunity for Danny, Wendy, and Jack to heal as a family. Danny believes that it's either the Overlook or "DIVORCE" (4.6), which is the most horrible thing he can imagine, at least before he experiences what the Overlook has to offer.
As horrors of the hotel increase with every tick of the clock, Danny sees he's made a dire mistake. In his tragically tender moment of realization, Danny exclaims, "(I'm just five! […] Doesn't it make any difference that I'm just five?)" (37.25-27). Well, yes and no. The horror genre thrives on dramatic irony. The protagonist in a horror story must act contrary to his or her own good through much of the story, while the readers cringe at each error. This heightens the readers' suspense, anxiety, and when done well, the readers' pity. It also mirrors real life to an extent. Humans in crisis situations often make the worst possible choices. So, yes, it does matter that Danny is only five, because he's even more vulnerable than the classic horror protagonist, and so even more intense emotions (perhaps) than usual are evoked in the reader. And, no, it doesn't matter, because he's a protagonist in a horror story; his job is to make mistakes, no matter how old he is.
That's what shining is on the surface, but it gets deeper, murkier, and more confusing the more we think about it. Some of the big questions arise when we think about the Overlook Hotel. For example, the hotel itself literally shines. When it fully comes to life on December 2, at midnight, all its lights come on, as Halloran observes when he arrives on his rescue mission. This is classic King logic – everything has a dark side, even the light. Every gift comes with a curse. In this case, the ability to shine brings with it a hypersensitivity to other psychic phenomena and paranormal activity. These phenomena can also be considered shining. Shining can manifest as good, evil, and ambiguous.
The relationships between those who shine and the Overlook is also food for thought. As we discuss in "Setting," the hotel is some kind of repository for evil. It seems to gain power from people who shine, because they can see what it is. Danny's ability is, apparently, extreme. So, the Overlook might be able to take over the world, or at least Colorado, if it manages to get the boy. Actually, we don't really know what will happen if it gets Danny, only that it wants him because he can shine so hard. Ultimately, the shining is something ambiguous, something that can't even necessarily be put in words. In "What's Up With Epigraph" and "Characters" we talk even more about shining (and there's definitely more to talk about) so check those out for a deeper look.