A bolo tie is a kind of necklace that cowboys and other people wear around their necks. It's made up of a string or cord, with a fancy decorative piece (often with a shape like a cowboy boot or a horseshoe) in the middle that sits at the base of your throat.
The string or cord usually has two metal ends with a small clasp, which is what holds the bolo in place on your neck. You can adjust the length of the string by pulling or loosening the metal clasps, so it fits just right.
Bolo ties are sometimes called "cowboy ties" or "string ties," and they're often worn with western-style clothing like cowboy hats, boots, and plaid shirts. People wear bolo ties for all kinds of occasions, from formal events like weddings to casual outings like going to the rodeo.