physical size of the screen measured by the diagonal.
Total number of pixels on the display
number of pixels per square inch of the display.
Display technology used in the smartphone. The display technologies decide a lot of factors including how it looks, what the brightness can be, the power consumption etc. Morden smartphone displays range from TFT, TN Panels to IPS LCD, OLED, and AMOLED panels.
Display shape with classification based on current trends. Morden displays come in different shapes and sizes and this varies from near bezel less, notch display, waterdrop notch, to fully bezel less phones. This lets one get an idea of how the display looks.
Percentage of display area to the front of the smartphone. This ratio became more popular recently with the introduction of tall 18:9 displays. Now we have bezel less, notched displays with screen to body ratios of 18.5:9, 19:9, and even 19.5:9.