1. A person that insists on being actively involved in a group conversation but is incapable of saying anything that adds any value.
The guy everyone wishes would just shut up and leave, because what they're talking about is actually interesting, and the constant "that's what she said"s stopped being funny about 12 minutes ago.
A social parasite that gets a little selfish boost of attention by sapping a little bit of energy out of any interesting discussion.
2. A person that does the equivalent of the above, except with the stock market.
Mike: "That's really cool, Sam, where do you work?"
Dan: "that's what she said!"
Sam: "Just two blocks away. We make the chess boards out of onyx, and marble"
Dan: "marble like my dick!"
Mike: "Neat, do you cut the stone with a water jet?"
Dan: "my dick's a water jet!"
Mike & Sam: "STFU
Dan! You are such a day trader! I hope you contract syphilis!"
A daytrader is a trader who buys and sells financial instruments (e.g. stocks, options, futures, derivatives, currencies) within the same trading day such that all positions will usually be closed before the market close of the trading day. This trading style is called day trading. Depending on one's trading strategy, it may range from several to hundreds of orders a day.
An institutional daytrader is a trader who works for a financial institution.
A retail daytrader is a trader who works for himself, or in partnership with a few other traders.
An auto trader is the person who performs auto-trading, which stands for automated trading and the use of computer programs and other tools to enter trading orders.