In the discussed article, "PC" stands for pseudo-center, which is used in the context of the PCASSO (Protein C-Alpha Secondary Structure Output) application. This method shifts the coordinates of Cα atoms to their pseudo-center position, defined as the center-of-geometry between consecutive Cα atoms. This adjustment aims to enhance the accuracy of secondary structure element (SSE) assignments by better representing the locations of backbone N-H/C=O atoms involved in secondary structure formation. The paper mentions a minimum cut-off distance of 6, but the maximum cut-off distance is not specified, suggesting it may relate more to accuracy rather than a defined value. The term "cut-off" in the PCASSO algorithm likely refers to a threshold used in the analysis, although further clarification from specific sections of the paper is needed for a more precise understanding.