The use of a liquid biopsy to assess molecular residual disease (MRD) of solid tumors holds significant promise for improving outcomes for patients with cancer. Liquid biopsies are a minimally invasive approach for the identification of circulating tumor biomarkers through a simple blood sample. Assays capable of detecting MRD through analysis of circulating tumor DNA (ctDNA) are rapidly evolving for clinical study applications and therapeutic interventions. To address these opportunities, BLOODPAC-a multi-disciplinary consortium representing stakeholders from public, industry, academia, and regulatory agencies-formulated a lexicon that provides a shared framework and clear definitions using liquid biopsies for solid tumor MRD with an emphasis on ctDNA detection. The terms in the lexicon are categorized under general MRD, ctDNA testing methodologies, reporting results, and acquisition timepoints, including examples of current and potential clinical use cases for MRD tests. The overall goal is to provide a unified language and approaches to solid tumor MRD to advance applications of these technologies, allow data aggregation to strengthen future evidence, and facilitate regulatory approvals, leading to the use of liquid biopsy as an early endpoint in clinical trials. We believe that a common set of terminology and methods for solid tumor MRD can improve understanding and appropriate use of testing, accelerate clinical development, and improve outcomes for cancer patients.