Shortening of kthxbye, which is in turn a shortened form of "k thx bye". The K is short for OK, which is short for "oll korrect", which is a facetious alteration of "All Correct". Thx is short for "thanx" which is a facetious alteration of thanks which is short for "Thank You". "Bye" is short for goodbye, which is an alteration of "God Be With You". "ktb" is the pinnacle of English's advancement, shortening "All correct, Thank you, God be with you." into three letters. Humanity is doomed. Obviously, it is used to end a conversation *fast* that you don't want to be in anymore.

The safeguarding of Earth and other worlds from biological cross-contamination (i.e. billionaires with too much time on their hands).

Also known as “planetary protection.” Planetary protection / quarantine “reflects both the unknown nature of the space environment and the desire of the scientific community to preserve the pristine nature of celestial bodies until they can be studied in detail.”

There are two types of interplanetary contamination. Forward contamination is the transfer of viable organisms from Earth to another celestial body. Back contamination is the transfer of extraterrestrial organisms, if such exist, back to the Earth's biosphere.

an abbreviation for wordkthxbye mostly used in losing an argument or just to sound cool.

Kill that bitch or kill this bitch.

"Killing the Bugs"

short for "keep texas brutal!"

The abbreviation for a KFC-Taco Bell.