Some windows, like programs like Notepad and Paint, have single panes. Other windows, like folders like my pictures and the search results, have multiple panes. Sometimes you can change the panes.
A program like Notepad has a single pane that you can write notes in.
A program like Paint has a single pane that you can draw pictures in.
This completes single panes.
A folder like your pictures has multiple panes.
A folder like the search results has multiple panes, too.
You can change the panes in the search results.
This completes multiple panes.