What he means is that static buy orders have variable range set by the bidder. Most putters don't want to have to travel more than a system. However, sometimes buy orders are set regionwide, which means you, the seller, can take the offer anywhere.
The immediate sell order option is not always terribly useful, nor practical.
Try setting a couple experimental longer term sell/buy orders and you'll see what I mean. Select the item you wish to buy more of, and right click it. Then you select the market view optio. You can also get to this screen with the buy or sell option by clicking the magnifying glass. In the market menu, select the "place buy order" option between the top and bottom windows.
Top window is static sell orders, bottom is buy orders. You can filter these to get an idea of what the local mean price is, or you can review the history and draw your own conclusions. Orders in the bottom window highlighted in green are orders that you can fill from your current location.
There is a range tab at the bottom of the buy order option. It is set to station by default, meaning only those who wish to sell that item in your station will be able to do so.
There's more in the Guide