Metacognition refers to higher order thinking which involves active control over the cognitive processes engaged in learning. Activities such as planning how to approach a given learning task, monitoring comprehension, and evaluating progress toward the completion of a task are metacognitive in nature. In other words, metacognition is "thinking about thinking" or understanding one's own thought processes.
I thought this article on "learning about learning" gave some really good tips on teaching metacognition in the classroom https://www.youtube.com/watch?v=E8klKdhNop8. The video answers a question that his students started to come to him and ask. The question asked by students is "how do I learn?", or " how do I learn correctly?", or "how do I learn differently?" and the link provides tips that might help.
I have noticed metacognition techniques used in the math class I am observing. At the beginning of class the teacher handed out a worksheet on the terms they will need to know for the geometry section they will be doing for the next couple of weeks. The vocabulary list was a list of 50 geometry terms that they had to look up and write down the definition for on their worksheet. Now, to have to write down 50 definitions in one night, or even two nights is a lot of work. She told them if they did 9 definitions a night, it would be way more doable, and they would have it complete by the day it was due. She continued on with her lesson, and left them the last 20 minutes to work on the homework from the book. She noticed that some of the students got done really quickly and just put everything away and were doing nothing. She let them know if they started on their vocabulary list it would mean less work that night, or could even possibly just split it up into less definitions to write per night. She was teaching them to self-regulate. It is very neat for me to think that I can teach my students other things to help them in their future aside from math.