In 1752, Benjamin Franklin conducted his famous kite flying experiments and proved that lightning is electricity. On his end of the string he attached a key, and he tied it to a post with a silk thread.Franklin noticed the loose fibers on the string stretching out; he then brought his hand close to the key and a spark jumped the gap. The rain which had fallen during the storm had soaked the line and made it conductive. http://en.wikipedia.org/wiki/Benjamin_Franklin#Inventions_and_scientific_inquiries
Charles Francois du Fay discovered that electricity comes in two forms which he called resinous(-)and vitreous(+). Benjamin Franklin and Ebenezer Kinnersley later renamed the two forms as positive and negative.
William Gilbert invented the term electricity
William Gilbert, scientist and physician to Queen Elizabeth I, invented the term electricity (from the Greek word for amber, elecktra). He was the first person to describe the earth's magnetic field and to realise that there is a relationship between magnetism and electricity.