Handheld digital audio recorders go by a number of different names: handheld field recorder, handheld recorder, portable digital audio recorder, and probably others.
No matter what you call them, these things are awesome!
They have built-in microphones, but also include various inputs and outputs for multiple sources including microphones, instruments, headphones, and more.
You can also use them as USB audio interfaces directly into your computer or as an on-camera microphone or on-camera mixer/interface.
The audio quality and flexibility are what really makes them worth it.
There are a couple popular brands that stand out in this space so most of the recommendations will be from the same few companies. I’m going to focus on portable recorders that include mic inputs so you can use separate interview-style microphones or plug in your studio XLR mics.
Top choice for most people: Zoom H4N Pro
If you want a more simple “grab and go” option, take a look at the Zoom H1n or the TASCAM DR-05 below. Or another budget-friendly option I would recommend if you have an iPhone is to look at these external lightning mics.