Reborrowing is when words of a certain language are borrowed into a different language, when the new language creates new words using the loanwords or roots they borrowed, and either when the newly created words are introduced to the language that the old loanwords came from.
Examples of this can be found in many languages.
From Greek to English, and back into GreekEdit
English uses many loanwords borrowed from French, Latin, and Greek, which is why many scientific words are made using words and word roots from these same languages. For example, the word "telegram" comes from the Greek roots "tele-", which means "distant/far", and "-gram/-graph", which means "writing", thus a telegram is a machine that sends written messages from far away. This word came back into Greek as τηλεγράφημα telegráfima.