This is a vim syntax file for PlantUML.

The filetype will be set to plantuml for *.pu, *.uml, *.puml, *.iuml or *.plantuml files or if the first line of a file contains @startuml.

Additionally the makeprg is set to plantuml assuming you have this executable in your path. This file could contain something like

#!/bin/bash
java -jar $HOME/lib/java/plantuml.jar -tsvg $@

You can change the name of this file by setting g:plantuml_executable_script and disable this feature by setting g:plantuml_set_makeprg to 0.

See examples here: Plantuml Syntax.