Hi Martin, it is a tqdm parameter (the default ProgressBar in pytorch lightning is unfortunately relying on tqdm). This is from the tqdm docs:
dynamic_ncols : bool, optional If set, constantly altersncolsandnrowsto the environment (allowing for window resizes) [default: False]. nrows : int, optional The screen height. If specified, hides nested bars outside this bound. If unspecified, attempts to use environment height. The fallback is 20. ncols : int, optional The width of the entire output message. If specified, dynamically resizes the progressbar to stay within this bound. If unspecified, attempts to use environment width. The fallback is a meter width of 10 and no limit for the counter and statistics. If 0, will not print any meter (only stats).