It refers to 2 distinct things, the process of communication and the technology of communication. It might be interesting to have your students look up the definition in a few different dictionaries to see what common elements are contained in each. The types of communication pictured are only a few of many different types. Petroglyphs are rock paintings left by ancient peoples on the walls of caves and mountains all over the world. They were probably originally painted as a parts of sacred ceremonies and to commemorate events like hunts.
Sign language is used by hearing impaired and deaf people all over the world.
Just like oral languages there are many different sign languages. Dog whistle s are used to train and call dogs. Dogs have better hearing than humans, which means they can hear sounds which we cannot. Dog whistles are designed to emit a sound in frequencies only dogs can hear.