I received this question today through the blog so I thought I would answer it here.
I use the term to refer to texts written by authors who claimed to be someone that they were not (i.e. in the same way that we use the term now). So whomever wrote the inauthentic letters attributed to Ignatius of Antioch was forging them in his name.
Sometimes I use the term more broadly – in the same way that the famous scholar of Christian hagiography Hippolyte Delehaye did in his Legends of the Saints - to refer to texts that have no basis in historical events.
I agree with Delehaye that the practice of inventing stories or weaving them together from other stories was generally more acceptable in antiquity than it is today. I would not condemn ancient authors for fabricating stories and texts, but I’m cautious about using these texts to make positive assertions about ancient history.