Flexbox
In plain terms
A CSS layout model for arranging items in one dimension.
Going deeper
Flexbox lays out elements in a row or column with flexible sizing, alignment, and spacing. It simplified once-painful layout tasks.
Under the hood
Excels at one-dimensional distribution and alignment; pairs with CSS Grid (two-dimensional) for full layouts.
Examples
Navbars, button rows, centering content, responsive component layouts.
Think of it like...
Like elastic shelves that stretch and space items evenly along a single axis.