The translation of yakitori is literally a grilled bird. This has meant that many people assume that yakitori is only used in reference to grilled chicken. However, in Japan, yakitori restaurants also serve pork yakitori.
It is more common to find chicken being served when you eat yakitori, and certainly, this is what is served from street food vendors. However, you can also find pork, especially pork ribs being served in the same style.
You may find chicken breast pieces, chicken thighs, chicken livers, and even chicken hearts being served in this skewered style. Yakitori, whether that be chicken or pork, is seasoned with tare sauce which is made from sake, mirin, soy sauce, and sugar.