Requirements articulating the needs of stakeholders are critical to successful system development and key to influencing their long-term effects. As the concept of sustainability has entered the discourse of a number of software-related computing fields, so has the term 'sustainability requirement'. However, it is unclear whether sustainability requirements areand should be different from how we already understand softwarerequirements. This paper presents the results of a corpus assisted discourse analysis study that explored the concept of sustainability requirements in order to understand how the term is being used in software and requirements engineeringand related fields. The results of this study reveal that theterm 'sustainability requirement' is generally used ambiguously and reveals significant segmentation across different fields. Ourdetailed analysis of selected influential papers highlights the segmented use of the term and suggests key focus questions that need to be addressed to establish a shared operative understanding of the term.