Virtualization renders only visible items in a list. Critical for thousands of items.
Problem: Rendering , DOM nodes is slow and memory-intensive.
Solution: Only render items in viewport plus buffer.
How it works:
Calculate which items are visible
Render only those items
Position items absolutely in a scrollable container
Recalculate on scroll
Libraries: react-window, react-virtualized, TanStack Virtual.
Interview tip: Always mention virtualization when discussing feeds or long lists.