CellBuffer is a logical grid of cells containing content to display on screen. It uses double buffering which can be used to reduce redrawing content on screen, which can have a very noticeable impact on performance and responsiveness.
Cell represents the contents of a single character cell on screen, or in some cases two adjacent cells. Terminals are expected to have a uniform display width for each cell, and to have a fixed number of cell columsn and rows. (We assume fixed pitch fonts.) The occasion when a double wide character is present occurs for certain East Asian characters that require twice as much horizontal space to display as others. (This can also occur with some emoji.)