When Blender crashes, I see in the console that it is “writing” a crash text file in the /tmp file directory. What is this file meant for, aside from being on your computer? It seems to be an error log of some sort. I am no developer or app programmer, so I can’t fix bugs in Blender’s code.
It’s an error log for troubleshooting. It tells you why it crashed so you can avoid the problem next time
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It’s primarily meant for you to attach to bugs that you file (Help → Report a bug). We will ask you to attach it when you file a bug about blender crashing.
It tells us the last function that was executed in both c++ and python and that sometimes helps us find the actual problem faster or duplicate it to another bug with the same information in their crash files.
Ah, is that why.
I thought Blender was written in Python, not C++! If you type in an invalid number into a value entry field like a letter X, it will say something like " Traceback most recent call last. File: . at line [number]. TypeError:"
Sorry, I couldnt remember more of what happens when you mistype a number value as a string. That comes from within Blender code itself, not any code I write, and is normal.
Python is used in many places indeed, primarily to define the UI layout, as an expression parser for input fields (like you mention), and of course the primary way to create Addons. But the implementation of the layout, and the functions that the Addons call, are mostly in C/C++. Same for all the geometry/image/simulation/rendering features everywhere else.
All in all, it’s a large portion but not the majority. Current stats from the git repository are as follows: C++:43.8%, C:40.7%, Python:11.4%, GLSL:1.7% etc.
So, if Blender crashed due to me cranking up the Hair particles on a cube up to like 100000 in a stress test, then I would be able to submit such a thing, or if I tried to do a fluid simulation and Blender crashed, then I would be able to find where it crashed and what I was doing in that situation just seconds before the crash, and submit it using Report a Bug?
The way apps crash so suddenly on macOS freaks me out. On Windows, it simply comes up as [app name has stopped working] whereas on older versions of Windows it says [App name has encountered a problem and needs to close. We are sorry for the inconvenience.] This happened many times on Windows XP and Blender 2.45, but on macOS, it simply says [App name quit unexpectedly] or on older versions of macOS it will say [The application name] quit unexpectedly, both error variants have a 
icon and a crash log of some sort, asking to “provide any steps to reproduce the problem”. I dread crashes when rigging objects because there is currently no way to “skin” armatures and verts on the GPU - this would eliminate crashes, so its very hit and miss.
You can read about how to file bugs here: https://wiki.blender.org/wiki/Process/Bug_Reports
We can only fix the bugs we know about. So give it a try if you experience a crash.