It is a lesion that may have originated due to frequent, repeated scraping of the epidermal, and/or keratin resulting in a type of proliferative lesion. Metal feeders that restrict the space in which the beak can poke through can be a predisposing factor, as well as birds housed in any wire enclosure where they may attempt to poke their beak through. Application of an antibacterial ointment or cream, and correction of whatever is causing the problem is suggested for treatment. If you notice a proliferation in the mass, as well as spreading, it could be a viral-related disease such as pox.