Front-End Development is the development of the parts of a website users see and interact with in the browser.
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
A developer builds a booking form whose labels remain readable on a phone, whose errors identify the missing field, and whose controls work with a keyboard. Those browser-facing elements are front-end development.