What is the meaning of Telegraph?

Synonym of telegraphy, any process for transmitting arbitrarily long messages over a long distance using a symbolic code.

The electrical device gradually developed in the early 19th century to transmit messages (telegrams) using Morse code; the entire system used to transmit its messages including overhead lines and transoceanic cables.

A visible or audible cue that indicates to an opponent the action that a character is about to take.

To use a telegraph.

To clearly communicate to another nonverbally, whether by gesture, a change in attitude, or any other sign, especially unintentionally.

Source: wiktionary.org