It's a topic that's difficult to put into words, true. I don't agree that "letting go" or "looking inward" are meaningless. In fact, letting go has a very literal meaning. You're supposed to not think about something on purpose, and when thoughts come, you don't follow them.

Looking inward is basically not focusing on the outside world. You're not supposed to sit and stare at a chair, but focus on something that is "inward", which could be for example your presence or your breathing.

Unclear terminology sometimes comes from either not having a deep enough grasp of the topic at hand. Sometimes on the other hand, the thing you're trying to explain is just hard to put into words.