This parameter controls the size of a file that is allowed to be passed through [[This Is Your Brain On Informatics: NGINX|NGINX]]. If a file that is passed to the server is too large, an error of 413 (or something similar will result). The way to fix that is to change the size of the file that is allowed to be passed to a larger number. The letter following that number will determine the units where the default (no letter) is bytes, ''k'' is for kilobytes , and ''m'' is for megabytes (you should not be passing gigabytes to your poor overworked server).