A selfie is a self-portrait photograph, typically taken with a hand-held digital camera or camera phone. When there is nobody around and you want to take a picture of your own, this picture is called a selfie.I am sure the word is derived ( originated) from " self": as a noun it means "the person that someone normally or truly is".
A hashtag is a word or ap hrase prefixed with the hash character, #, to form a label. It is a tag. Words or phrases in messages social networking services such as Facebook, Google+, Instagram, Twitter, or VK may be tagged by entering # before themThe term hashtag can also refer to the hash symbol itself when used in the context of a hashtag