Bar tack is a series of hand or machine made stitch

Stitch (textile arts)

In the textile arts, a stitch is a single turn or loop of thread or yarn. Stitches are the fundamental elements of sewing, knitting, embroidery, crochet, and needle lace-making, whether by hand or machine...

es used for reinforcing areas of stress on a garment, such as pocket

Pocket

A pocket is a bag- or envelope-like receptacle either fastened to or inserted in an article of clothing to hold small items. Pockets may also be attached to luggage, backpacks, and similar items...

 openings, bottom of a fly

Fly (clothing)

A fly on clothing is a covering over an opening join concealing the mechanism, such as a zip, velcro or buttons, used to join the opening. The term is most frequently applied to a short opening over the groin in trousers, shorts and other garments, which makes them easier to put on or take off and...

 opening or buttonhole

Buttonhole

Buttonholes are holes in fabric which allow buttons to pass through, securing one piece of the fabric to another. The raw edges of a buttonhole are usually finished with stitching. This may be done either by hand or by a sewing machine. Some forms of button, such as a Mandarin button, use a loop...

s. It consists of a series of close-set zig-zag stitches (machine) or whip stitches (hand), usually 1/16"-1/8" in width and 1/4"-3/8" in length. In denim

Denim

Denim is a rugged cotton twill textile, in which the weft passes under two or more warp threads. This produces the familiar diagonal ribbing identifiable on the reverse of the fabric, which distinguishes denim from cotton duck. Denim has been in American usage since the late 18th century...

 jeans

Jeans

Jeans are trousers made from denim. Some of the earliest American blue jeans were made by Jacob Davis, Calvin Rogers, and Levi Strauss in 1873. Starting in the 1950s, jeans, originally designed for cowboys, became popular among teenagers. Historic brands include Levi's, Lee, and Wrangler...

, it is often in a contrasting color, such as orange or white.