This paper focuses on a critical yet often overlooked aspect of data in digital systems and services-deletion. Through a review of existing literature we highlight the challenges that user face when attempting to delete data from systems and services, the lack of transparency in how such requests are handled or processed and the lack of clear assurance that the data has been deleted. We highlight that this not only impacts users' agency over their data but also poses issues with regards to compliance with fundamental legal rights such as the right to be forgotten. We propose a new paradign-explainable deletion-to improve users' agency and control over their data and enable systems to deliver effective assurance, transparency and compliance. We discuss the properties required of such explanations and their relevance and benefit for various individuals and groups involved or having an interest in data deletion processes and implications. We discuss various design implications pertaining to explainable deletion and present a research agenda for the community.