A "plain english" no nonsense definition goes a long way to introduce your concept. Save the fancy technical jargon for further down in the README if you must.
Specialized terminology allows the communication of complex concepts compactly. For the specialists a brief description like you mentioned is perfect. If you give it first, that person can read it and decide.
It should certainly be followed by a tear down or other plain English explanation of what the thing is.
Kind of like: ``` Brief
A little longer
Be descriptive about the thing
Go into every detail you want to discuss about the thing in the repository... ```
The jargon fooled blurb makes a great "a little longer" and gets out of the way to let the more readable description be given. Burying that can be a pain.
I need to either find or write a good readme template with that in mind.
The times when I need to read the repo README is when I am not familiar with what I am looking for. I say err on the side on more documentation, err on the side of a better explanation.