Shika is one of the positions in a Zen temple. It's the sixth position of the Rokuchoshu (six positions of lead monks). Formerly, it was called "Shihin."
A shika is chosen from among the monks who have trained for more years than others. The shika takes care of guests from outside, takes care of monks newly entered, and so on. Today, the details of the position differ slightly between the Rinzai/Obaku sects and the Soto sect. In the Rinzai/Obaku sects, the shika is also often appointed as the fusu, who assists the chief priest and supervises the monks. In the Soto sect, the shika mainly takes care of guests and new monks.
In the Rinzai sect, "shika" is the name of a position as well as the rank of priest.