C-AF Sensitivity lets you choose how rapidly the camera responds to changes in the distance to the subject while focusing with continuous AF [C-AF].
Choose a higher value for higher autofocus sensitivity, a lower value to prevent the camera refocusing on objects that briefly obscure the subject.
Choose higher values to autofocus track subjects that are moving toward or away from the camera or changing speed unpredictably or subjects that suddenly enter the frame. Choose lower values to prevent the camera refocusing in environments where the subject is briefly obscured by other objects or to prevent the camera focusing on the background when you are unable to keep the AF target positioned over the subject.