Double glazed windows are named as such because of its two panes of glass in between the frame. One type of design is Sash windows - read more here: What Does Double Glazing Cost?
A gap within these panes is filled with air for insulation to keep the heat and cold inside the home
Sliding windows are longer horizontally and slide horizontally. There is no hinge. Because gravity does not force the window down, there is no pressure on the spring, which means less wear and tear.