If translation is the art of transposing a written text from a source language to a target language, interpreting is only spoken.
The exercise consists in translating orally the speech of a person segment by segment as it unfolds. The interpreter intervenes immediately after the speaker has paused. This technique, unlike simultaneous interpretation, does not require any special equipment.
It practices in a low voice. While the speaker and the participants speak normally. The interpreter is whispering in the ear of his client.