The Outsiders is an examination of 1960's youth culture and the effects of peer pressure on young men.
Slang has evolved and changed significantly in the decades following the Second World War. Many words that were common are now obscenities, while others that were shocking are now commonplace. One example of how context shifts over time is the word "weed." Once meaning only an undesirable plant which spreads and blocks productive crops, it has become common vernacular for any form of marijuana, alongside "pot," "dope," "ganja," "bash," and many others which have evolved over time. However, the word did not always mean marijuana, instead existing briefly before the heydays of the 1960s hippie as a common term for a simple tobacco cigarette. This is an example of how something seen as rebellious and cool becomes "normal" or boring, and is then appropriated to the next rebellion: in this case, the rebellion of smoking tobacco became so commonplace that the slang term "weed" changed to mean the even more culturally scandalous marijuana cigarette.
"Wish I had me a weed." My knees were shaking as I finished drying off, sitting there in my jeans.
"You want to see a movie before we go see Johnny and Dallas?"
"Nope," I said, lighting up another weed. I still had a headache, but I felt better... that way you could tell the other guy was human too.
(Hinton, The Outsiders, amazon.com)
Written in the 1960s, the novel is set in the mid-1950s, when the stereotypical "greaser" character was a young, rebellious male with greased hair, a fast car, and a leather jacket. Before the 1960s marijuana was not as commonplace nor as culturally negative, and smoking tobacco cigarettes was seen as edgy and cool. Cultured men smoked pipes or cigars, while the cigarette still held a stigma of poverty, and so embodied the anti-authoritarian stance of the greaser. In the novel, "a weed" is a tobacco cigarette, which is smoked more for effect than for nicotine addiction; its use here is to show how the young characters in the novel show bravado while hiding their insecurities and immature fears.