ICO stands for Initial Coin Offering. it is a slight change from IPO Initial Public Offering on the stock markets. At first there were only clones of bitcoin being released, but now it has progressed to tokens on the Etherium network. The term is now used for both alt-coins and tokens. These events are getting a lot of attention because Millions of dollars are being raised for these groups, so with only a white paper and no proof of concept.
Here’s a great interview from MadBitcoins on the current ICO market.