Tapestry Needles have a long eye and a blunt tip and are used for counted thread work such as cross stitch,  blackwork and needlepoint or any needlework on fabric that has open holes that shows where each stitch is placed. The blunt tip of the needle helps when stitching as the needle pulls the thread smoothly through the holes without a sharp tip to catch on the fabric.
Tapestry needles come in sizes 13 to 28 with 13 being the largest and 28 the finest , so you would use the lower sizes with the lower count of fabric and the higher sizes with the higher count of fabric.

 I usually recommend a 24 for 14 and 16 count or a 26 for 18 count.