Frequency as in what you are currently in acceptance with. We passively accept that we are alive. But mind, subscribe to various ideas. That derives your future outcome of what you may experience and due to which state of mind you are in.
It's a metaphorical method of suggesting two minds are in tune with one another. Women who can finish their partner's sentences, or people who share a similar thought, independently of one another, etc. You'd say, "Hey, our frequencies aligned," or, "It seems like we're tuned into each other." I've said it myself on occasion. It basically means you share similar thoughts, a common worldview.
I remember seeing a guy on tv talking about it and he just seemed to be treating "frequency" as synonymous with "wave" and would have sounded a little less like a crackpot if he did say "wave"
