4K refers to a display resolution that is approximately 4000 pixels wide. Specifically, it typically denotes a resolution of 3840 x 2160 pixels, which is also known as Ultra High Definition (UHD). This resolution is four times the number of pixels found in Full HD (1920 x 1080 pixels), offering much sharper and more detailed images.

4K displays can be found in various types of display technologies, including:

1. LCD (Liquid Crystal Display): These are the most common types of 4K displays. They use a backlight to illuminate liquid crystals that manipulate light to create images. LCDs can be further categorized into:

   • IPS (In-Plane Switching): Known for better color accuracy and wider viewing angles.
   • VA (Vertical Alignment): Offers better contrast ratios but may have narrower viewing angles.
   • TN (Twisted Nematic): Typically faster response times but poorer color reproduction and viewing angles compared to IPS and VA.

2. LED (Light Emitting Diode): Technically, these are a type of LCD display where the backlight is provided by LEDs. They are often marketed as LED displays but are fundamentally LCDs with LED backlighting.

3. OLED (Organic Light Emitting Diode): These displays use organic compounds that emit light when an electric current is applied. Each pixel in an OLED display generates its own light, allowing for true blacks and infinite contrast ratios. OLED 4K displays are known for their superior picture quality, including better color accuracy, deeper blacks, and wider viewing angles.

4. QLED (Quantum Dot LED): These are a type of LED display that uses quantum dots to enhance color and brightness. QLED 4K displays can produce a wider color gamut and higher peak brightness compared to standard LED displays.

5. MicroLED: This is an emerging technology where each pixel is a microscopic LED. MicroLED 4K displays promise the benefits of OLED (like true blacks and high contrast) without the risk of burn-in, and they can achieve higher brightness levels.

6. Projection: 4K resolution is also available in projectors, which can display 4K content on large screens. These can use different technologies like DLP (Digital Light Processing), LCoS (Liquid Crystal on Silicon), or laser projection.

Each of these display technologies has its own advantages and trade-offs in terms of picture quality, response time, viewing angles, color accuracy, and price. The choice of a 4K display depends on the specific needs and preferences of the user, such as whether they prioritize color accuracy, contrast, response time, or cost.