Homemade spice blends have been closely guarded family secrets and have flavored Middle Eastern food since the middle ages. As with many regional blends there are countless versions that vary from region to region, village to village and even family to family.
Za'atar is also known as Zaatar, Zahatar Za'tar and Zahatar. This seasoning is a delightful blend of dried herbs, sesame seeds, and sumac, and usually salt. The regional variations can be quite different - think of it like the various salsas that we use in the US. While there is no right or wrong salsa practically everybody can find a variation they like best (chunky, with black beans, hot, mild, etc.).