Press B to soft-select vertices, faces, or edges
Soft Selection lets you select vertices, edges, faces, UVs, or even multiple meshes in an organic way. It's useful for making smooth slopes or contours on your model without having to transform each vertex manually. Alternatively, you could also use Sculpting to accomplish the same effect.
It works by maintaining a falloff from the selected components to the components around your selection to create smooth transitions. For example, if you select a vertex at the center of a plane and translate it up into a spike without Soft Selection, the sides are very steep and the point is very sharp. When Soft Selection is on, the slope and tip are smoother.
To soft select components on a NURBS or polygon mesh
The falloff area is represented by a color gradient. The gradient is applied to all of the components that are within the falloff area.
B-drag to resize the selection area
All components within the falloff area are selected and the selected transform tool manipulator appears.