A 3D lenticular picture can display depth in full sharpness only for a certain depth. The center of the sharply displayed zone is determined by the photography process, and can be located anywhere in the scene. This phenomenon is very similar to common photography, in which there is also a certain zone in which the image is sharp. In common photography the depth of this zone is called "depth-of-field".
The mechanism which gives rise to blurring outside the sharply imaged zone is different in common photography and 3D lenticular picture, but the visual effect is the same. Therefore, we call the depth of the sharply imaged zone in a lenticular picture by the same name.
The depth-of-field of a 3D lenticular picture is a primary figure of merit, and is determined by the limitations of the printing technology. It also depends on the lenticular lens characteristics. Estimates of several depth-of-field values for pictures printed using an inkjet printer and different lenses are given in my book. The values range between a few millimeters in thin lenses to a few hundreds of millimeters in thick ones.