What is "yerkish"

Yerkish is an artificial language developed for use by non-human primates. It employs a keyboard whose keys contain lexigrams, symbols corresponding to objects or ideas.

A lexigram represents a word but is not necessarily indicative of the object which the word refers to. Lexigrams were notably used by the Georgia State University Language Research Center to communicate with bonobos and chimpanzees. Researchers and primates were able to communicate using lexigram boards made in up to three panels with a total of 384 keys.