Hi, a buy wall is a very large amount of Bitcoin placed in the buys side of a coin listed on any exchange. It can be there for a number of reasons. Perhaps to encourage the price to rise, or an investor who really wants to buy in to a coin cheaper than what they are on the sell side. I usually see it as encouraging sign. A sell wall works in the opposite way (depending on its size) but really large ones can often be used to suppress the price. It could even be placed by the same person who has the large buy wall so he can accumulate more coins cheaper than buying from the sells side. An ICO stand for initial coin offering. They are purchased by the public from the developers or an exchange before they are listed for regular trading. Etherium and Lisk are two examples. I like ICO's because I don't mine coins and it gives me a chance to get in early. However, they do come with risks like developers vanishing after they have received BTC from the public. You can usually tell from the announcement though if there is a risk. If there is very low effort put in to the ICO caution is advised.
thanks
GailSan pretty much nailed it, but I will add to be sure to use his definitions and not those you typically find on trollbox chat. I get sick of people calling a 10, 20 even 50 BTC order a wall like you often see, especially on Poloniex. "OMG guys, there is a 20 BTC buy wall on ETH" is typical of this type of talk. A real buy (or sell) wall would be more on the order of 1000's of BTC considering ETH's volume and would take hours, if not days to move past.
Most of what you do see of these big walls are fake, meaning that they are meant more to move the market in a direction (buy up, sell down) then actually acquire or sell coins at the "wall's" price. You can tell this as if a wall is nibbled on, meaning some orders against it are executing, the wall suddenly disappears without the corresponding amount of orders showing in the history, meaning the manipulator removed the order before it was completely filled.
