Two-dimensional embroidery is a flat embroidery technique with a large number of stitches per inch (SPI). Because many stitches (density) are used, the embroidery gets a rich and luxurious look.

Three-dimensional embroidery has a high relief.
This can be achieved by overlapping multiple stitches. For larger surfaces, a rubber filler (template) is used, the stitches are placed over this.

An appliqué is a technique in which we use fabric layers in combination with embroidery. An appliqué is somewhat like a patch. A good example are the large letters you see on American college jackets.