The word ukulele in Hawaiian means jumping flea. The term is used to refer to a musical string instrument (plucked, nylon stringed instrument usually played with the bare thumb and/or fingertips, or a felt pick). Today the ukulele is used worldwide. It is featured in TV shows, movies, opera, etc. and is especially poplar with millions of individuals in the countries of Japan, Canada, the United Kingdom, and the United States.

In the 19th century, a former British army officer named Edward Purvis was living in Hawaii. He became an official at the royal court of King Kalakaua. Purvis was given the Hawaiian nickname of 'Ukulele'. He was considered to be a small and lively person and therefore, he was called Ukulele ("jumping flea") by friends and others.

When Portuguese immigrants arrived in the Hawaiian Islands in 1879, they brought several of their native musical instruments. One of the instruments was a small four-stringed guitar. Purvis liked this new instrument. He learned to play it. In time the small guitar became a general favorite with everyone on the islands. It took the nickname ukulele of the man (Purvis) who had made it popular and had completely incorporated its use in and outside of the Hawaiian society.

More Info: en.wikipedia.org