A pixel is the smallest dot of colour in a digital image — the building block of every photo, every frame of every video, every UI element on your screen. The word is short for "picture element". Zoom into any image far enough and you'll see the grid of pixels that make it up.
Each pixel doesn't store a single colour; it stores three or four numbers — one for the red, green and blue intensity (and sometimes a fourth for transparency). The number of distinct values each component can take is the bit-depth: 8-bit means 256 levels per component, 10-bit means 1024 levels, which matters a lot for smooth gradients and HDR.
Two practical takeaways. First, pixel count drives data volume — going from HD (≈ 2 million pixels) to 4K (≈ 8 million pixels) is a 4× increase, and bandwidth and storage scale roughly the same. Second, more pixels only help if the source had enough detail to begin with; upscaling old footage to 4K stretches the same information across more pixels, not the other way around.
