limit - Limits a string to a certain number of characters. Defaults to 100. [[+description:limit=`50`]]
http://rtfm.modx.com/display/revolution20/Input+and+Output+Filters+%28Output+Modifiers%29#InputandOutputFilters%28OutputModifiers%29-Stringoutputmodifiers
The output modifiers act like a mini-language within MODx tags, and are extremely useful. Just don't go crazy with them, as too many of them can slow down a page load.