Selenium trioxide is a chemical compound with the formula SeO3. It appears as a colorless, oily liquid and is known for its strong oxidizing properties. This compound is primarily used in the production of selenium compounds and as a reagent in various chemical reactions. When exposed to moisture, selenium trioxide can form selenium dioxide and sulfuric acid, making it a hazardous material. It is important to handle it with care, as it can cause severe burns and respiratory issues. Proper safety measures should be taken when working with this compound in laboratory or industrial settings.