CSV means comma separated values. It's like a normal "txt" file with commas at regular places to separate some values. Typically the first line of CSV file is a "header", containing names of columns ...
circuitdigest_preprocess_comment(Array, 'comment', Array) call_user_func_array('circuitdigest_preprocess_comment', Array) (Line: 261) Drupal\Core\Theme\ThemeManager ...