DragAndDrop is a global front end option that specifies whether to allow drag-and-drop editing.

DSolve[eqn, y, x] solves a differential equation for the function y, with independent variable x. DSolve[{eqn_1, eqn_2, ...}, {y_1, y_2, ...}, x] solves a list of ...

Dt[f, x] gives the total derivative d f/d x. Dt[f] gives the total differential d f. Dt[f, {x, n}] gives the multiple derivative d^n f/d x^n. Dt[f, x_1, x_2, ...] gives d/d ...

DumpSave["file.mx", symbol] writes definitions associated with a symbol to a file in internal Mathematica format. DumpSave["file.mx", " context`"] writes out definitions ...

DynamicEvaluationTimeout is an option for displayed objects, cells, and notebooks that specifies the timeout in seconds for any Dynamic computations they contain.

DynamicModule[{x, y, ...}, expr] represents an object which maintains the same local instance of the symbols x, y, ... in the course of all evaluations of Dynamic objects in ...

DynamicModuleValues is an option for DynamicModule that stores downvalues of local symbols.

Dynamic[expr] represents an object that displays as the dynamically updated current value of expr. If the displayed form of Dynamic[expr] is interactively changed or edited, ...

DynamicWrapper[e, expr] represents an object that displays as e, but dynamically updates the expression expr whenever that object is visible on screen.

EdgeCount[g] gives a count of the number of edges in the graph g.EdgeCount[g, patt] gives a count of the number of edges that match the pattern patt.