What ⌉ means
It closes the right side of a ceiling pair.
In a formula, the right ceiling symbol ⌉ closes ⌈x⌉, which means the smallest integer greater than or equal to x. Its partner ⌈ opens the expression. In LaTeX, \rceil and \lceil are the right and left commands.
Ceiling brackets grew out of older integer-part notation. Gauss used square brackets, [x], for the greatest integer at most x in 1808. Kenneth Iverson introduced the half-bracket forms and the names floor and ceiling in his 1962 book A Programming Language, making each operation's direction visible.
It is a delimiter, not a broken square bracket
⌉ is intentionally just the upper-right corner of a tall, narrow mathematical delimiter, not a damaged square bracket. By itself, it does not mean “round up”; the full ceiling operation needs ⌈ around the expression.
Don't confuse it with
1Combination ideas
2Questions people ask
1Why does ⌉ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ⌉
⌉\2309Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.