I see 30 hits from monkey mind, searching for Both words, not either word. If we come up with a good concise definition and what to do about monkey mind, I'll add it to the Glossary. It's a subject that certainly belongs there, but which is not there now, sorry to say. I looked at the pertinent monkey mind hits on this sites and also looked at some other sites for monkey mind. The undisciplined mind is like a monkey, chattering constantly, always seeking input.
Meditation is the process of calming and training the monkey to be still.
One of the hardest things for people to do is give up the workings of the mind while in the relaxation response. NO frustration, NO anger at self for monkey mind, etc., just go back to the technique. This, too, shall pass. The average person has about 15,000 random thoughts every day . . . Those thoughts become emotions . . .