Nikon D5500 - Manual (Page 108)

84 More on Photography
A
AF-Area Mode
AF-area mode selections made in shooting modes other than P, S, A, or
M
are reset when another shooting mode is selected.
A 3D-Tracking
If subject leaves the viewfinder, remove your finger from the shutter-
release button and recompose the photograph with the subject in the
selected focus point. Note that when the shutter-release button is
pressed halfway, the colors in the area surrounding the focus point are
stored in the camera. Consequently 3D-tracking may not produce the
desired results with subjects that are the same color as the
background.