Kinesthetic motor imagery (KMI) is a specific kind of imagination. Namely, you imagine how your body would feel when performing some action, without actually performing it. A kind of internal miming.
I formulated this concept to myself a few months ago without knowing the name, and just now found that it has a name in neuroscience. In this post I want to tell you that KMI is really cool and can be used for many things. Here's some ways I've been using it:
Language learning. Most of my German learning, once I got past the basics, has been listening to German audiobooks and miming the feeling of speaking the words as I listen. This can be done for long stretches of time without much effort, and when coupled with a little bit of actual speaking, seems to improve language skills pretty fast. What's more, the skills improve together: I pick up words, sentence structure, accent and inflection all at once.
Music learning. My saxophone practice is mostly listening to a jazz tune and imagining the feelings of playing each phrase, in my mouth position and breathing and so on. Sometimes I'll pause the recording and try to repeat a little bit on my saxophone, imitating the tone, articulation and everything. I don't make many attempts to get it right, just try a couple times and go back to listening; it seems my playing improves over time anyway, as I get more and more things right.
Social manners. When I'm outside or at some gathering, I sometimes take a quick look at the people around me, and try to imagine in my body how it would feel to stand, walk, or talk like this or that person at the moment. Nothing too detailed, no trying too hard, just quick impressions. I've found that being around strangers in this way is calming, and they seem to see me in a more laid back way as well. Also I've found that some people look relaxed on the surface, but imitating them makes me feel like they're tense about something, almost as if I'm mind reading; while some other people are exceptionally peaceful and fun to imitate.
Looking online, it seems people are also using KMI in sports, to learn or practice various movements. I wouldn't know, but it seems plausible. Part of the magic of KMI, to me, is that you don't get hung up on details: you first get a blurry picture of how an action would feel overall, and then the details gradually fade in over time. Which is exactly how physical skills are supposed to be learned, I think.