There are two sections to the Editor Status bar: the left section provides information either about the current state of the topic, or about the task you're performing; the right section describes the book filtering that's being done if you're using variants.
Information about the topic or task
File object, Hyperlink, or Embedded Topic information
If your cursor is on a hyperlink, an embedded topic, or an image, the Description and ID number of that object are displayed.
Character Style and Paragraph Style
Name of the paragraph and/or character style at the current cursor position. When a character style is used, the name is displayed to the left of the paragraph style name.
Click on the pop-up selector to the left of the slider to choose a zoom option (from 25% to 200%).
Zoom Control Slider
The Topic Editor Zoom Control is used to change the display of the topic's content, making it smaller or larger.
Information about the book
The book section of the status bar shows the name of the book and the filtering that has been applied to the book's content. The filtering can be applied if you are using a book with variants. All criteria values that have been used are shown to the right of the filter icon.