In sewing, to tack or baste is to make quick, temporary stitching intended to be removed. Tacking is used in a variety of ways:
Basting thread on the right side (outer side) of fabric.
Tracing paper from a pattern is basted to fabric before a piece is cut. The basting marks are outlined with tailor's chalk.
Tailor's tacks mark fabric to trace a pattern piece, without attaching tracing paper.