█ is known as a full block or full box. It can be written as "▮" in HTML or typed on Microsoft Windows with Alt +25881. Its Unicode character is U+2588, an industry standard. █ has unlimited uses. For example, it can be used to designate something blocked out, or even to make graphic designs in the style of ASCII art.
1 To type a Unicode symbol in Microsoft Windows, hold down the ALT key and enter the code provided
using the numeric keypad.