Examples of metalloids are boron, germanium, arsenic, silicon, tellurium, polonium and antimony. These elements exist in the realm between metals and non-metals and can have properties of both.
Scientists agree that "metalloid" is a vague term, and even an element usually thought of as a true metal, such as aluminum, might be classified as a metalloid.
Often metalloids have the luster of metal but are brittle in a way that real metals are not. They can generally be alloyed with metals and are useful as semiconductors and flame retardants. They're also used in fireworks, signal lights and flares.
Some metalloids, taken in trace amounts, support good health. These include silicon, boron, and even arsenic in incredibly tiny amounts, though arsenic in any appreciable quantity is toxic. Boron and silicon are used as insecticides, and both have medical applications. Boron in the form of boric acid can treat infections and silicone gel treats burns.
Most metalloid oxides can be used to make glass. Boron trioxide is used to make glass ovenware, while silicon dioxide has long been used to make regular glass.
Silicon is famous as a semiconductor. At first, germanium was used as a semiconductor till silicon proved less expensive, easier to work with and better able to tolerate high temperatures.