HTML entities.

Why entities exist

Some characters can't be written directly in HTML because they mean something to the markup itself. The clearest example is < — type a literal less-than sign and the browser thinks a tag is starting. Entities are the escape hatch: < renders as a visible < without breaking anything. The same goes for the ampersand, the greater-than sign and quotes inside attributes. Beyond those required four, entities also let you insert symbols that aren't on the keyboard — copyright, em dashes, arrows, currency and accented letters.

Named vs numbered

Every entity has two forms: a named one like © that's easy to read, and a numbered one like © that works for any Unicode character. Named entities are nicer to write but only exist for a limited set; numbered entities cover everything. For modern pages saved as UTF-8 you can often just paste the real character, but entities remain the safe, unambiguous choice — especially for the reserved characters, which you should always escape. To convert formatted text to HTML, try the Markdown to HTML tool.