Buy to open

Buy To Open - To establish an options position by going long. Read the Buy To Open tutorial.
C
Call -see Call Option.

BUY - buy to open a long position, specify quantity and price type
SELLSTOP - sell to exit a long position, specify the selling price type
BUYMORE - buy to add to a long position, specify a quantity and price type ...

The terms "buy to open", "buy to close" sound like they are part of your broker's application to place orders? I wouldn't say that these terms are "standard".

Consequently, a "buy to open" order is always used to open a long position. Sell To Open An order entered to establish a new short position. Generally used in futures/options investing to distinguish between establishing vs. closing a position.

See also: Short, Contract, Issue, Shares, Right