HTML is HyperText Markup Language, the foundational markup language used to define the structure and meaning of web content.
It matters because development decisions affect speed, security, scalability, tracking, SEO, and maintenance. A site that looks good but is fragile or hard to update can quietly hold back every marketing channel.
Example
An article uses one main heading, section headings, paragraphs, and a list of steps. HTML identifies those structures so browsers and assistive technology can interpret them; it does not determine every visual style.