Ahint or memory prompt that us to recall something we've forgotten is called a

The correct answer is a mnemonic device.

A mnemonic device refers to any memory enhancement technique that helps us encode and remember information. A common example of a mnemonic device is using the sentence "My very educated mother just showed us nine planets " to remember the names of the planets in the solar system. The first letter of each of the words in the sentence corresponds to the letters each of the planet's name begins with (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Pluto).