Generally only for Bass cabinets. A reflex cabinet is one where you have the speaker facing the back of the cabinet and holes in the top and bottom of the cabinet to reflect the sound out.
A refrain is a line that is repeated from verse to verse. In other words, a Refrain is NOT a section. It is fundamentally part of a verse. Usually, though not always, at the end of every verse. Often it contains the hook/title and tends to be the most memorable part of the song.
The refrain is intended to be the most memorable part of the song. It is repeated several times so that it sticks in your mind.
Generally in a guitar called a Dobro. Resonators are the cymbal looking pieces in the center of a guitar which adds a higher frequency to the sound. These are used a lot for “slide guitar parts.
This is multiple sound images, of an original source sound, blended together at the point of listening. The multiple images are caused by the reflection of the sound from walls and other surfaces or artificially created using electrical or mechanical reverberation units. See the Songstuff article on Reverb by following the link below.