Greek Small Letter Eta η

The Greek Small Letter Eta character (η) is a standard HTML entity defined in the HTML specification. In HTML source code, it can be written using the named entity reference η, the decimal numeric character reference η, or the hexadecimal numeric reference η. The character is assigned Unicode code point U+03B7 in the Universal Character Set.

Eta is the seventh letter of the Greek alphabet, commonly representing efficiency in engineering and physics. It also denotes viscosity in fluid dynamics, the Dedekind eta function in mathematics, and the learning rate in machine learning gradient descent algorithms.

Greek letter entities are indispensable for scientific papers, engineering documentation, statistical analyses, and mathematical content published on the web. From physics equations using alpha and omega to statistical formulas featuring sigma and mu, these entities allow content authors to include Greek characters reliably without requiring specialized fonts or complex Unicode input methods on the keyboard.

When deciding how to encode the Greek Small Letter Eta character in your HTML documents, the named entity η is generally the most readable choice for developers reviewing or maintaining source code. The decimal form η and hexadecimal form η 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 eta entity in engineering content (efficiency η), fluid dynamics (viscosity), machine learning documentation (learning rate η), and quantum mechanics. It is widely used across scientific disciplines and has become common in AI and deep learning literature.