Summary view is unique in that it includes text and thumbnail images (if images, or news items with images, are present). Descriptions are included, as well.
The icons, "author" and "modified" columns are only visible to users who're logged in.
Thumbnail view works well for image libraries.
Standard view is the default display view for folder contents. It lists all published content within the folder, with descriptions, if present. Icons are only visible to logged-in uers.
Select (or Change) Content Item as Default View
Unlike the other display options, selecting a content item allows you to choose a single piece to show in place of the folder contents. This is useful for setting a custom landing or home page.