This method restores the L global variable to the original value it had before Leaflet inclusion, and returns the real Leaflet namespace so you can put it elsewhere, like this:

// L points to some other library
// you include Leaflet, it replaces the L variable to Leaflet namespace

var Leaflet = L.noConflict();
// now L points to that other library again, and you can use Leaflet.Map etc.