A more thorough explanation:

Definition: Dictation is the act of speaking words that are then written down by someone else. The written words are also called dictation.

Examples:

• During the meeting, the boss gave dictation to his secretary, who wrote down everything he said.
• The teacher asked the students to take dictation of the passage she read aloud.

The first example shows how dictation is used in a workplace setting. The boss speaks and the secretary writes down what he says. The second example shows how dictation is used in a classroom setting. The teacher reads a passage and the students write down what she says.