1. What does it mean?
딸피 describes a character whose remaining health is extremely low. Players use it to warn teammates, describe a narrow escape, or note that an opponent is nearly defeated.
Also written or said as 실피, ttalpi
2. The nuance
Outside games it has also been used as a demeaning label for older people. That age-based use is insulting; the examples here are about game health, not people or life expectancy.
3. Examples
“딸피로 살아남아서 회복 아이템을 찾았어.”
I survived with almost no health and looked for a healing item.
“상대가 딸피여도 무리해서 쫓아가지는 마.”
Even if the opponent is low on health, don't chase recklessly.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.