According to wikipedia, the meaning of selfie is a genre of self-portrait photograph, typically taken with a hand-held digital camera or camera phone. Selfies are often associated with social networking and photo sharing services such as MySpace, Facebook and Instagram, where they are commonly posted. They are often casual, are typically taken either with a camera held at arms length or in a mirror, and may include only the photographer or other people as well. Or in simplified definition its a "picture taken of yourself".
Here are some examples of selfie: