jquery-flex | A fluid asymmetrical animated grid plugin for jQuery | Plugin library

'resize.flexImages' is just a string that represents an event type in the DOM - it's being used in that script to begin the name of the event that is being bound to the event handler function, in this case function(){ makeGrid(grid, items, o); } during the on() function call.

The .off() function call doesn't specify a handler function, as it is presumably already bound/attached to that event during the on() call - which again is specified as a string. The off() just removes the handler.

If you read the documentation here: https://api.jquery.com/on/ you will see jQuery recommends this convention for naming the event so it doesn't interfere with other events, in this example, presumably other resize events.

An event name can be qualified by event namespaces that simplify removing or triggering the event. For example, "click.myPlugin.simple" defines both the myPlugin and simple namespaces for this particular click event. A click event handler attached via that string could be removed with .off("click.myPlugin") or .off("click.simple") without disturbing other click handlers attached to the elements. Namespaces are similar to CSS classes in that they are not hierarchical; only one name needs to match. Namespaces should contain upper/lowercase letters and digits only.

... From the jQuery docs