Well theyre called shark fins or winglets, the latest ones are blended into the wing but older aircraft had them retro-fitted. They reduce drag on the wing tips by minimising the vortices. Its been a long known phenomena but its only recently that commercial aircraft have had them fitted after they realised what a significant amount of fuel they saved and how much they could increase payload. Your Easyjet A320s have them too :-)
Thank you for enabling me once more and its only fair as its needlework monday tomorrow :-)
Hope you're having a great weekend :-)