No-mind means intelligence.  And when I am asking you for gibberish, I am simply asking you to throw out the mind and all its activity so you remain behind - pure, clean, transparent, perceptive.

Osho, This. This. A Thousand Times This, Ch. 6

Osho first introduced the No-Mind meditation as part of his evening discourses on Zen. Later on, it became a group process, lasting for two hours a day for seven days. For the first hour, participants do gibberish. For the second hour, they sit silently, doing nothing.

    
        

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Here is an excerpt from the talk where Osho first introduced the meditation:

The first part is gibberish. The word 'gibberish' comes from a Sufi mystic, Jabbar. Jabbar never spoke any language, he just uttered nonsense. Still he had thousands of disciples because what he was saying was, "Your mind is nothing but gibberish. Put it aside and you will have a taste of your own being."

To use gibberish, don't say things which are meaningful, don't use the language that you know. Use Chinese, if you don't know Chinese. Use Japanese if you don't know Japanese. Don't use German if you know German. For the first time have a freedom - the same as all the birds have. Simply allow whatever comes to your mind without bothering about its rationality, reasonability, meaning, significance - just the way the birds are doing. For the first part, leave language and mind aside.

Out of this will arise the second part, a great silence in which you have to close your eyes and freeze your body, all its movements, gather your energy within yourself. Remain here and now.

Osho, Excerpted from the series, Live Zen and reprinted in Meditation: The First and Last Freedom