Textblock is formed by sheets that are attached on one side (sewn, wired, or glued). Covers are attached to the textblock.
The used evaluation method considers front sheets as belonging to the textblock; i.e. their condition is evaluated together with the textblock. The end leaf is the sheet that is glued or sewn to the first and the last sheet of the book (with single fold); the end leaves join the textblock and the covers. It is often decorated, marbled etc.