Just as an application is a collection of sheets, a sheet is a collection of objects that can be customized and manipulated to facilitate analyzing the data. Each sheet may, and probably will, look different given that Qlik Sense provides a blank canvas on which to place objects:

The preceding screenshot is a sheet contained in the Qlik Sense Sales Discovery demo application. This sheet has filter boxes down the left side, some Key Performance Indicator (KPI) objects oriented vertically in the center, a combo chart featuring three different sales metrics broken out by the Region field, and a line chart of Sales by day at the bottom.