In years gone by most people had single glazed windows, which contained one sheet of glass. In time these traditional, wooden windows will need replacing; when the time comes to do this we now tend to replace them with double-glazing instead.
Double glazed windows contain sealed units which are made from two panes of glass. These have a gap in between them that provides good insulation against the cold in winter and helps to keep the heat inside the house when you need it most.
