What 슬 means
By itself, 슬 is a Korean syllable, not a whole word.
Hangul blocks join consonant and vowel letters into a written syllable. Here, 슬 begins 슬프다, the Korean word for “sad”; the complete word—not 슬 on its own—carries that meaning.
The Korean alphabet Hangul was created in 1443. A guide called Hunminjeongeum explained the new writing system in 1446. It addressed a practical problem: Korean differed from Chinese, and Chinese-character-based methods for writing Korean were difficult for many people to use.
Repeated in 슬슬, the syllable is part of an adverb whose sense depends on the verb: it can describe acting slowly, gently, quietly, or indirectly.
Alone, it reads as Korean text or a syllable fragment; the surrounding word carries the meaning.
Do not translate 슬 alone as “sad”; that meaning belongs to 슬프다.
What it means when someone sends it to you
3 readingsQuestions people ask
1Why does 슬 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 슬
슬\C2ACCodes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.