DependentVariables is an option which specifies the list of all objects that should be considered as dependent variables in equations that have been supplied.

Deployed is an option for displayed objects, cells, and notebooks that specifies whether their contents should be considered deployed, so that elements such as Slider, ...

DepthFirstScan[g, s, {"event_1" -> f_1, "event_2" -> f_2, ...}] performs a depth-first scan of the graph g starting at the vertex s and evaluates f_i whenever "event_i" ...

DerivativeFilter[image, {n_1, n_2}] computes the n_i\[Null]^th derivative of image in the vertical and horizontal directions.DerivativeFilter[image, {n_1, n_2}, \[Sigma]] ...

f' represents the derivative of a function f of one argument. Derivative[n_1, n_2, ...][f] is the general form, representing a function obtained from f by differentiating n_1 ...

DesignMatrix[{{x_11, x_12, ..., y_1}, {x_21, x_22, ..., y_2}, ...}, {f_1, f_2, ...}, {x_1, x_2, ...}] constructs the design matrix for the linear model \[Beta]_0 + \[Beta]_1 ...

DiacriticalPositioning is an option for UnderscriptBox and related boxes that specifies how close diacritical characters are drawn to the base character.

Dialog[] initiates a dialog. Dialog[expr] initiates a dialog with expr as the current value of %.

DialogNotebook[{cell_1, cell_2, ...}] represents a dialog notebook that can be manipulated by the Mathematica front end.

DialogProlog is an option for Dialog that can give an expression to evaluate before the dialog starts.