Intel's chips have letters like "K" and "U" after the numbers that give you an idea of what kind of purpose and performance the computer is designed for.
Some computers have Intel chips without any letters. Those are the standard, base chip models.
The "K" chips are usually the fastest, with higher clock speeds than the standard chips without a letter in Intel's mainstream chips. It also means the chip is "unlocked," where its clock speeds can be tweaked — or "overclocked — by a user to squeeze out a little extra performance than what you get out of the box. Usually, it's mostly enthusiasts who tend to overclock their chips, and they're mostly designed for desktops or high-performance laptops.
The "G" means the chip has a built-in graphics processor. Most of Intel's chips come with basic built-in graphics processors so you can display something on your monitor without an entirely separate graphics card. But Intel's "G" processors come with a more powerful graphics processor for more power-hungry apps and games. Surprisingly, the graphics processors in Intel's "G" chips come from the company's main rival, AMD.
The "T" means the chips is designed to use less power while also having less performance than the standard chips without any letters.
The "U" means the chip is designed for laptops and mobile devices, as "U" chips are Intel's "ultra-low power" models. They're "low power" because they use even less power than the "T" models and have slower clock speeds than their full-size, non "U" equivalents. By having slower clock speeds, they don't get as hot and have a lower risk of heat-related damage. That's good for thin laptops that have limited cooling compared to larger desktops and laptops.
You can find more information about Intel's chip letters on Intel's site, where it shows what other letters mean on previous generation chips.