Main video on Track V1 Live response clip on track V2
Use a Size, Position & Rotate filter (with keyframes) to resize and animate the Live response clip.
Look for Shotcut tutorials on Video overlay and keyframes for more info.
“Jump cut” or “hard cut” if clips are jammed against each other with no transition. If there is a transition between clips, then call it whatever the type of transition is.
If it’s a video clip on top, it’s called a video overlay or picture-in-picture.
If it’s an image on top, it’s called a graphic overlay.
What type do you need? Lavalier, boundary, shotgun, wireless, dynamic, condenser, XLR, USB? For general purpose stuff when portability is important, I am happy with the Rode VideoMicro.