The stick in the middle is the mast. The grey sail to the left of the mast is the main sail. The green sail on the boat on the left is a jib and the blue sail on the boat on the right is a genoa (also known as a genny/jenny). 


The difference is whether or not the sail overlaps the mast. A jib will fit inside the foretriangle (triangle between the mast, deck and forestay). If it overlaps then it’s a genoa. If it doesn’t it’s a jib. Genoas are categorized by the percentage of overlap so a 150% genoa has 50% of it’s area behind the mast when fully flying. 


Now you know.