Judging by my findings, 'atraque' means 'backstitching', though seams are usually secured as they're sewn, not after the garment is finished.

http://www.proz.com/kudoz/spanish_to_english/textiles_clothi...

http://forum.wordreference.com/showthread.php?t=109493

http://www.proz.com/kudoz/spanish_to_english/other/1575452-a...

When you sew there is a starting and an ending point. Have you ever had the seam start to unravel or the thread come loose so the stitching shows as lines of thread at what is supposed to be a seam? Learn to back stitch or lock stitch to secure the beginning and end of your sewing to prevent them from unraveling or from the stitching loosening up and stretching out of shape.

http://sewing.about.com/od/beginner1/ss/How-To-Back-Stitch-A...

In the UK, people usually refer to 'backstitching' but maybe 'back tacking' is more common in the US.

Sew the seam, remembering to back tack and the beginning and end of the seam and removing the pins as you go. Once you have sewn the seam, snip off the loose threads at each end.

http://www.angelaosborn.com.au/sew-straight-seams/

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Note added at 47 mins (2013-12-29 01:52:56 GMT)
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Reading my last reference, 'atraque' could mean everything related to securing a seam, including cutting off the loose threads, which I think would be far more logical in this case.

Who hasn't bought a garment that has the odd piece of cotton dangling from a seam?