Lethal Move (살인기, Sal-ingi) is a term used in the technique naming system. It literally means "Kill Person Technique" in Korean.
There is no explanation of how techniques with this name differ from others, but from the meaning, it is presumed they are used with the intention to kill.
An example would be Rapid-Fire Shinsu Cannon, where the same technique used by Baam against Data Zahard did not contain "Lethal Move" in its name, while Yu Han Sung used the Lethal Move version when attacking rankers in the Last Station.
Currently, the user with most Lethal Moves is White, with five Lethal Moves.
Almost all known users are Rankers, with the exception of
- Khun Ran, who used the Maschenny-style technique against Cassano and Anak
- Data Zahard, who used Rampage against Baam.
- Twenty-Fifth Baam, who used Lethal Move version of Floral Butterfly Piercing Technique against a canine ranker. 
List of Lethal Moves
The list may be incomplete, as not all technique names are recorded in full on wiki.
LINE Webtoon translations