No not a lesson in hurling insults, in this case bagging out describes the sewing of two pieces of fabric together and then turning them right side out.
A new pattern I'm working on called the APRON TOP includes the option of adding front pockets which I recommend bagging out before attaching; here's how I did it.
1. Cut out the outer and inner pocket pieces and press.
2. To form a crisp top edge, with right sides together stitch the outer and inner pockets together using a 1.5cm seam allowance.
3. Press the seam allowances toward the inner side and then, on the right side, make a line of stitching close to the seam.
4. Fold along the top edge and pin with right sides together. Using a 1cm seam allowance stitch around the outside edge leaving a small opening in the bottom of the pocket.
5. Clip the top corners and around the curves. Cut away half of the inner seam allowance so the edges are uneven.
6. Turn the pocket right side out through the small opening in the bottom edge. Carefully push out the corners and then press.
7. I added a line of heavy top stitching across the top of my pockets. The pockets are now ready to stitch on. Pin in place, try on and check in the mirror to make sure you're happy with the final position. Stitch evenly around the sides and bottom close to the edge and you're all done.
Both of the fabrics used in this example are from Liberty.