A tack is a short nail with a broad, flat head, especially one that is used for fastening carpets to the floor.

If you tack something to a surface, you pin it there with tacks or drawing pins.

If you change tack or try a different tack, you try a different method for dealing with a situation.

If a sailing boat is tacking or if the people in it tack it, it is sailing towards a particular point in a series of sideways movements rather than in a straight line.

If you tack pieces of material together, you sew them together with big, loose stitches in order to hold them firmly or check that they fit, before sewing them properly.