I'm not sure why the flalign environment seems to have become very fashionable. Here are two solutions, based on the alignedat inner environment.
Inside the equation* or flalign* environment (if you really want left alignment) I define a local abbreviation for the labels. If you have several of these constructions, move the command in the preamble, so you're sure that you always have the same typesetting.
The labels should be left aligned, as they are the leftmost column in a table. I also provided two alternative ways for typesetting angles in degrees; I'd avoid the explicit ^{\circ} in any case in the document body.
\documentclass{article} \usepackage{amsmath} \usepackage{siunitx} \usepackage{lipsum} % to add context \newcommand{\dg}{^{\circ}} \newcommand{\Ang}[1]{% \SI[retain-explicit-plus]{#1}{\degree}% } \begin{document} \lipsum*[2] \begin{equation*} \newcommand{\tcond}[1]{\text{\textit{#1}:}\quad}% a handy abbreviation \!\begin{alignedat}{3} &\tcond{Angle} & -45\dg &\le \theta &&\le +45\dg \\ &\tcond{Bins} & -135\dg &< \theta && < -45\dg \\ &\tcond{Slant} & +45\dg &< \theta &&< +135\dg \\ &\tcond{Tilt} & -180\dg &\le \theta &&\le -135\dg \quad\text{or}\quad {+}135\dg \le \theta \le +180\dg \end{alignedat} \end{equation*} \lipsum*[2] \begin{flalign*} \newcommand{\tcond}[1]{\text{\textit{#1}:}\quad}% a handy abbreviation \!\begin{alignedat}{3} &\tcond{Angle} & \Ang{ -45} &\le \theta &&\le \Ang{+45} \\ &\tcond{Bins} & \Ang{-135} &< \theta && < \Ang{ -45} \\ &\tcond{Slant} & \Ang{ +45} &< \theta &&< \Ang{+135} \\ &\tcond{Tilt} & \Ang{-180} &\le \theta &&\le \Ang{-135} \quad\text{or}\quad \Ang{+135} \le \theta \le \Ang{+180} \end{alignedat}&& \end{flalign*} \end{document}
