What Is Retina Display?

A Retina display is Apple’s marketing/trademark term for a screen whose pixel density is high enough that individual pixels are not discernible at a typical viewing distance (so text and graphics look “print-like” and edges look smooth). It’s not a single fixed PPI number—the required pixel density depends on viewing distance and screen size.

The engineering meaning (what it really implies)

• Human “20/20” visual acuity is often approximated as being able to resolve about 1 arc-minute, which corresponds to roughly ~60 pixels per degree (PPD) for pixel-level detail.
• Apple popularized this idea publicly with iPhone 4, describing a threshold around ~300 PPI at ~10–12 inches viewing distance (a rule of thumb, not a hard physiological limit).

Practical impact in products (HiDPI)

Apple typically achieves “Retina” behavior by using HiDPI scaling:

• UI is laid out in points (logical pixels), while the panel has 2× or 3× more physical pixels per point.
• This is why you see asset naming like @1x, @2x, @3x in Apple platforms.

What “Retina” is not

• It’s not the same as “4K/8K” (which are fixed pixel-count standards).
• It’s a perceptual threshold tied to angular resolution (PPD) and how far you view the display, not just raw resolution.

If you tell me the device type and typical viewing distance (phone, laptop, monitor, VR), I can estimate the PPD/PPI needed to meet a “retina-like” threshold for that use case.