Rajas means strips in Spanish, but they're specifically strips of roasted and peeled poblano chiles. I love them.
Roast a bunch of poblanos till they're black. I just set them directly over the flame on the gas stove, or you can broil them (put them as close to the element as possible), or when I have an electric stove, I roast them in a cast iron pan over high heat. No matter what you do, turn them so they blacken evenly. Stick the blackened peppers in a plastic bag and close it, or put them in a bowl and cover with a towel to steam for about 10 minutes. The black skins will be easier to pull off. Get most of the black off (you can rinse them to make it easier, but you'll lose a little flavor). It's okay to have a little skin left on there.
Then slice them into strips and use them in recipes calling for rajas.