A ‘pull back’ approach refers to states taking measures to prevent migrants from leaving their country of origin e.g., aiding developmental projects, increasing border security at the country of origin, information campaigns about migration risks/consequences, etc.
A 'push back' approach refers to states taking measures to increase immigration control near or at their own borders e.g., strict border control/surveillance, tackling human trafficking/smuggling gangs, returning migrants, signing deals with third party countries, limiting access to state resources, etc.
An undocumented migrant does NOT include those who are under review in the asylum seeker process.