According to the Oxford Dictionaries the word of the year for 2015 is not a word at all but an emoji, specifically the ‘Face with Tears of Joy’:
Do you use emoji(s)?
Is the plural emoji or emojis?
Do you think of them as words?
What’s your word of the year?
I use “emoji” singular, “emojis” for a specific plural (“she signed the text with three emojis”), and “emoji” as a general mass noun (“the use of emoji is sweeping the world”).
According to ALDictionary most search word is “bling”.
After thinking it over, I might personally go with a related word I learned a few months ago: mojibake. Borrowed from Japanese (in kanji/kana, it’s 文字化け), it means the garbled output from a computer program when it tries to process text with the wrong encoding.