master-detail typically involves a table where more detail is shown about the selected row.
Clasically in master-detail a small number of rows of a table are shown and then below the table more detail for the selected row - all fitting above the fold.
It doesn't have to be that way. An in-line more accordion-like display is possible.
Common problems are making sure that the detail panel is clearly associated with the selected row. A suggestion in the referenced question is that a color-tie with the selected row would help in this example.
In this question:
the detail panel is itself a list, so has variable size, and a list-in-list solution is discussed.
Questions about master detail also concern the behavior - thumbnails and full sized views of images ( Behavior of auto-scrolling gallery ) are a form of master-detail.
When there are multiple levels of master-detail, a tree-table may be used. This can be one factor that drives master detail designs to evolve into explorer-like designs, with a tree on the left and details on the right, as in these two questions, How would you handle user access management with 4 levels and 9+ unique roles? and exclusive select in a table: radio button, rowclick, text only, text and icon, or icon? - which also suggests the three panel view, tree-list-detail, as in mail browsers.
You can find lots of visual examples of master-detail displays by doing a google image search for "master detail". Master detail often arises in database backed applications from a JOIN on two tables.
Creating a Master-Details Question
When creating a 'Master-Details' question, be clear about the number of levels of detail, and whether the amount of detail is the same for all items or whether it varies. Also give some indication why the detail needs to be on the same page. In Google mail, details of messages navigate to a new page.