Metalloids, also known as semimetals, have properties that bridge the gap between metals and nonmetals. While it's hard to pinpoint exactly three properties that define all metalloids, here are three key characteristics that are common among them:

1. Semiconductor Behavior: This is arguably the most defining property of metalloids. They have an electrical conductivity that falls between metals (high conductivity) and nonmetals (low conductivity). Their conductivity can also be manipulated by factors like temperature or the addition of impurities, making them crucial for electronics.

2. Metallic Luster: Metalloids often exhibit a metallic sheen or luster, similar to metals. This is due to their ability to reflect light, although they may not be as shiny as true metals.

3. Variable Chemical Reactivity: Metalloids can act as both metals and nonmetals in chemical reactions, exhibiting varying degrees of reactivity depending on the specific element and the reaction conditions. For example, they can form both ionic and covalent compounds.

It's important to note that metalloids often have other properties that contribute to their unique nature. For example, they can be brittle and have a relatively high melting point, similar to metals.

While metalloids share these characteristics, it's also crucial to remember that each metalloid has its own unique set of properties.