The word bombilla comes from the Portuguese word for bulb (bombi). It is a sipping straw that has a strainer at the bottom that resembles a bulb. The strainer keeps the Yerba Mate from entering the sipping straw and being swallowed while drinking from the bombilla.
It comes in many different types materials beginning with the traditional cane or bamboo one to nickel-plated, Alpaca Silver and fine silver or stainless steel.
All are acceptable depending on your personal preference.
Many people have more than one bombilla for different uses such as for guests, at work, family, etc.