Buy Minus
  
Buy Minus refers to an order to buy a stock when it's below its current price.
The grammar is weird here, but you could remember it as "Buy when it's minus X dollars." A trader or investor might place this order if they're anticipating a drop in price, and want to be first in line to buy when it drops.
Generally, a couple things must happen for this order to be placed. The price of the share must be below the current market price, and the last trade on the share has to have been a minus buy as well.
It's like seeing a big screen TV on clearance at a department store, and knowing they have plenty in stock to unload before the new holiday inventory arrives (you have friend that works there, so you've got the inside scoop). You might decide, knowing they have a supply on hand and a limited time to sell it, to wait to buy until they drop the price a bit more. You know they might sell out faster than you anticipate, and you might not get a TV at all, but if you do...you'll get it at the price you wanted.
See Uptick Rule.
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Finance: What are Limit Order, Sell Limi...7 Views
Finance a la shmoop what is a limit order? you want to sell a thousand shares
of Colonel electric it was demoted after they cut their dividend the shares have [Scissors cuts dividend in half]
been trading wildly between $15 and $25 a share you don't want to feel like a
moron for having sold them at fifteen bucks when six weeks later they kissed
25 with tongue so what do you do well you put in a limit order that is you put
a limit of a minimum price of 25 bucks a share for Colonel Electric such that [Pile of stocks appear]
those shares will simply sit in your account unsold maybe forever until
somebody out in the wild blue yonder of Stockland is willing to pay twenty five [Woman standing at a colonel electric stand]
dollars or more for the shares where you have a minimum price limit of 25 bucks a
share in your order so here's to hoping they sell and don't get further demoted [Man carries stock into car]
Sargent Electric is just a place you don't want to go
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