According to Reference.com, the word kilo is a prefix meaning "one thousand" and is used in metric system measurements. Common examples include kilometers, kilograms and kilowatts, which represent one thousand meters, grams and watts respectively.
The prefix kilo comes from the Greek word "khilioi," which means "thousand". It was officially adopted as a metric system prefix in 1795 though it was in common use before that. It can be used as a standalone word to represent a measurement such as in the phrase "a kilo of cocaine" where the term kilo refers to one kilogram.
In computer terminology, a kilobyte is actually 1,024 bytes rather than 1,000 bytes. This is because computers use binary calculations, and 1,024 is equal to the number two to the 10th power.