A file with pawns of only one colour on it. This file is closed to the pawn owner, and open to the other player.
                                                            
                                                     
                        
                                                
                        
                        
                            A file on which only one player has no pawns.
                                                            
                                                     
                        
                                                
                        
                        
                            a file with pawns of only one colour. Look at the handouts on Rooks and, if you are brave, the Minority Attack section of the handout on Pawn mobility.