Window retainer clips are small, spring-loaded clips that help keep window panes in place. They are typically made of metal or plastic and are inserted into a groove in the window frame. When the window is closed, the clips engage with the pane, preventing it from moving out of place. Retainer clips are an important part of ensuring that windows are weathertight and secure. They are also relatively inexpensive and easy to install, making them a cost-effective way to maintain your windows.