# Definition with word to be defined instead of counter

I know the title is a bit weird but I'll try to explain it in a better way here. In the beginning of a chapter I'd like to define some basic terms. Currently I'm using

\newmdtheoremenv{mydef}{Definition}


which results in the following:

Is there an easy way to do it without "Definition 1." but "Machine Learning" ?

mdframed lacks the possibility to define unnumbered theorems, but it's not difficult to add it.

Next, a common trick for a variable label can be applied.

\documentclass{article}
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{mdframed}

\NewDocumentCommand\newmdtheoremenvnonumber{O{} m m }{%
\newtheorem*{#2}{#3}
\BeforeBeginEnvironment{#2}{%
\begin{mdframed}[#1]}%
\AfterEndEnvironment{#2}{%
\end{mdframed}}%
}

\newmdtheoremenvnonumber{mydefinner}{\mydeflabel}
\newcommand{\mydeflabel}{}
\newenvironment{mydef}[1]
{\renewcommand\mydeflabel{#1}\begin{mydefinner}}
{\end{mydefinner}}

\begin{document}

\begin{mydef}{Machine Learning}
Machine learning is the field of study that gives computers
the ability to learn without being explicitly programmed.
\end{mydef}

\end{document}