What 캡 means
It is a Korean syllable, not a word on its own. Say it roughly “kaep”; by itself it does not pick “cap,” “best,” or “hat.” Inside words it lends that sound, including the loanword “cap” in cap hats and air-cap packaging.
The block has no separate birth date. Hangul itself was completed in 1443 and promulgated in 1446 to make writing easy to learn and use. Unicode can store 캡 as one precomposed block or as the jamo sequence ㅋ+ㅐ+ㅂ without changing how it reads. A 1997 youth-slang survey recorded one phrase built from it as “the best.”
Neutral as a syllable; the praise use is informal, not formal Korean.
Do not read 캡 alone as “the best”; that meaning belongs to a phrase or context.
Combination ideas
3Questions people ask
1Why does 캡 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 캡
캡\CEA1Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.