Empty Set ∅

The Empty Set character (∅) is a standard HTML entity defined in the HTML specification. In HTML source code, it can be written using the named entity reference ∅, the decimal numeric character reference ∅, or the hexadecimal numeric reference ∅. The character is assigned Unicode code point U+2205 in the Universal Character Set.

The empty set symbol represents a set with no elements. It is one of the foundational concepts in set theory and appears throughout mathematical logic, computer science, and database theory. The symbol is a circle with a diagonal slash, distinct from the Scandinavian letter Ø.

Mathematical HTML entities enable web authors to display proper mathematical notation without relying on images or specialized rendering libraries like MathJax or KaTeX. While complex equations and multi-line formulas may still benefit from dedicated math typesetting tools, individual symbols expressed as HTML entities render quickly, remain accessible to screen readers, and can be styled with CSS just like regular text content.

When deciding how to encode the Empty Set character in your HTML documents, the named entity ∅ is generally the most readable choice for developers reviewing or maintaining source code. The decimal form ∅ and hexadecimal form ∅ are equally valid alternatives that work in contexts where named entities may not be supported, or when generating HTML output programmatically from server-side code. All three representations produce identical visual output in every modern web browser.

Use the empty set symbol in set theory discussions, database query results indicating no matches, and logical expressions. It is important to use the mathematical empty set character rather than the Scandinavian Ø, as they are semantically different characters despite their visual similarity.