A stirring rod or "stir rod" is a piece of laboratory equipment

Laboratory equipment

Laboratory equipment refers to the various tools and equipment used by scientists working in a laboratory. These include tools such as Bunsen burners, and microscopes as well as speciality equipment such as operant conditioning chambers, spectrophotometers and calorimeters...

 used to mix chemicals and liquids for laboratory purposes. They are usually made of solid glass, about the thickness and slightly longer than a drinking straw, with rounded ends.
Like most laboratory glass, stir rods are made of borosilicate (commonly known as pyrex).