C11 and D29 are cell addresses in a spreadsheet, specifically in Microsoft Excel.
C11 refers to the cell located in column C and row 11.
D29 refers to the cell located in column D and row 29.
Cell addresses are used to identify specific cells in a spreadsheet, and are typically written in the format "ColumnLetterRowNumber" (e.g., A1, B2, C3, etc.).