Definition:
A stylus is a writing utensil that is typically long and stiff, like a ballpoint pen.
In relation to a smartphone, a stylus is a small stick used to enter information or write on the touch screen of a phone.
Many smartphones, such as the Palm Treo Pro, include a stylus. The stylus usually slides into a slot built into the smartphone for that purpose. Some touch-screen phones, such as the iPhone, do not include a stylus, but you can purchase one separately. One example is the Pogo Stylus for iPhone, which snaps on to the side of the phone.