If the cutter and workpiece movements are in opposite directions, the milling process is known as - 

Explanation:​
Milling:

• Milling is a process of producing flat and complex shapes with the use of a multi-point (or multi-tooth) cutting tool. The axis of rotation of the cutting tool is perpendicular to the direction of feed, either parallel or perpendicular to the machined surface.
• Milling machines are superior to other machines in terms of accuracy and surface finish.

There are two basic types of milling operations:

Up milling / Conventional milling:

• The workpiece is moving towards the cutter, opposing the cutter's direction of rotation.
• The cutting force is minimum during the beginning of the cut and maximum at the end of the cut. 
• The thickness of the chip is zero at the start of the cut and increases to a maximum value just before the tooth disengages the workpiece.
• As the cutting force is directed upwards, it tends to lift the workpiece from the fixtures.

Down milling/ Climb milling: 

• The cutter rotation is in the same direction as the motion of the workpiece being fed.
• The cut starts with the full chip thickness.
• The cutting force is maximum at the beginning and minimum at the end of the cut.
• In down milling, the cutting force is directed onto the work table, which allows thinner parts to be machined without susceptibility to breakage, but it requires the optimum holding device as the cutting tool forces the workpiece in the opposite direction of the tool motion. Therefore the gap between the lead screw and the half nut increases which requires a backlash eliminator. 
• A better surface finish is obtained.