Three-quarter block

A text cell with three of its four quarters filled in.

Imagine the little rectangle one character occupies, split into four quarters. ▜ paints the top two and the lower-right one, leaving the lower-left corner blank. Unicode has a character for every such pattern: single quarters ▘▝▖▗, diagonals ▚▞, halves ▀▄▌▐, the three-quarter shapes ▛▜▙▟ and the full block █. Together they let one character stand in for four tiny pixels.

That is the whole point. A program or a device that can only print text can still draw a coarse picture by choosing the right block for each cell. Computer terminals and some 1980s home computers drew pictures this way, and the quadrant shapes were added to Unicode for compatibility with those terminal graphics, so such screens can be written as plain text. Today you meet ▜ in terminal programs (text-only command windows) that render images and charts, in text-mode games, and in text art posted on social media, where it is usually one piece of a bigger shape.

Why does ▜ look wrong or gappy on my screen?

Because every font draws block elements its own way.

In a fixed-width (monospace) terminal font, each cell is the same size and the blocks are normally cut to exact quarters, so neighbouring tiles touch and a picture looks solid. In the variable-width (proportional) fonts used by chat apps and web pages, the block may be narrower or taller than the cells around it, thin seams appear between tiles, and a drawing made of dozens of them loses its shape. If the font has no glyph at all, you see a hollow box or a question mark.

So if someone sends you a picture made of blocks and it looks like noise, the font is the usual culprit, though copying or line wrapping can scramble it too. Viewing it in a code editor or terminal with a fixed-width font, or asking for a screenshot, usually shows it as intended.