ok, i just read through this whole thread..... does anybody remember what the original post was?????? ok, the OP didn't seem to understand the use of the term "resonant frequency" applied to a low pass or high pass filter. the simple answer is "if you're talking about passive RL or RC filters, you're correct, they do not resonate, but once you combine R,L, and C elements in the filter (and that includes active feedback and amplification that substitutes for L or C), it has become a resonant circuit, even if the Q has been made less than 1. the L and C elements interact, and there will be a frequency where Xc and Xl are equal, and the circuit will be resonant."
i had a few good laughs while reading through the thread.... we as techs and engineers can be an opinionated bunch for sure..... and seem to enjoy going down rabbit trails.... the thread started as a question about how a certain term is used, and ended up as an argument about whether imaginary numbers were really imaginary (or maybe not)...... (on the other hand.....)