Edit Mesh > Slide Edge Tool

The Slide Edge Tool lets you reposition a selection of edges or entire edge loops on a polygon mesh. You can either select the edges individually by shift-selecting the edges or select an entire edge loop using the Select > Select Edge Loop Tool before using this tool. You can also convert an existing selection to an edge loop using Select > Convert Selection > To Edge Loop, or use the pickwalk feature (Left and right arrow hotkeys).

Use the middle-mouse button to slide the selected edges. The vertices associated with the selected edges move along their shared perpendicular edges. Alternately, you can press the Shift key to move the edges/edge loop along each vertex normal.

Edit Mesh > Slide Edge Tool >

Settings

Determines how the selected edges or edge loop gets repositioned. The options are Relative and Absolute.

Relative: Moves the selected edges/edge loop based on a percentage distance along the selected edge. For example, when you slide the edge loop to a location that is approximately halfway along the sliding edge, all the selected edges appear at a position that is halfway relative to their original position.
Absolute: Moves the selected edges/edge loop based on an absolute distance along the selected edge. When the distance along the sliding edges is highly variable, by default, the Slide Edge Tool uses the shortest edge to determine the maximum distance the edges/edge loop can be moved. This option can be useful when you want the edges/edge loop positioned at a specific distance from other existing edges.

Note
By default, the Slide Edge Tool stops sliding edges whenever the selected vertices touch the next vertices on the sliding edge. You can override this behavior by pressing the key so that the vertices move beyond.

Snapping Settings

Lets you adjust certain snapping specific options.

Use Snapping: Determines whether the snapping settings will be used. A checkmark specifies whether the Snapping Points and Spanning Tolerance is used.
Snapping Points: Controls the number of snapping points to which the sliding vertices will snap. The slider range is between 0 and 10. The default snapping point value is 1 which snaps to the midpoint.
Spanning Tolerance: Controls how close a vertex must be to a snapping point before the vertex snaps to it. The slider range is between 0 and 1. Set the value to 1 when you want to ensure the vertex always snaps to a snapping point.