Sheilaism is the name of a personal religion, invented by a woman named Sheila Larson. Her description of her faith in Robert Bellah's 1985 Habits of the Heart made her, and her religion, emblems of a particularly American mode of belief.
From p. 221 of Habits of the Heart:
"Sheila Larson is a young nurse who has received a good deal of therapy and describes her faith as "Sheilaism." This suggests the logical possibility of more than 235 million American religions, one for each of us. "I believe in God," Sheila says. "I am not a religious fanatic. [Notice at once that in our culture any strong statement of belief seems to imply fanaticism so you have to offset that.] I can't remember the last time I went to church. My faith has carried me a long way. It's Sheilaism. Just my own little voice." Sheila's faith has some tenets beyond belief in God, though not many. In defining what she calls "my own Sheilaism," she said: "It's just try to love yourself and be gentle with yourself. You know, I guess, take care of each other. I think God would want us to take care of each other." Like many others, Sheila would be willing to endorse few more specific points."