Acorn-computer terminology for a software interrupt. Pronounced "swai" apparently, although myself and my friends could never get out of the habit of pronouncing it "swee".
In BBC BASIC 5 on the ARM-based Acorn machines the equivalent keyword was SYS, which took either a numeric parameter or a string symbolic name. Operating system extensions were allowed to add their own symbolic names into the global namespace which allowed code like SYS "EqWimp_SetIconText", "iconname", "Hello" to be written - a user-friendly way of calling directly into the OS or on of the extensions.