From UNHRC's 2015 report
Refugees: I"Individuals recognized under the 1951 Convention relating to the status of refugees, its 1967 Protocol, the 1969 organization of African unity (OAU) Convention Governing the specific Aspects of refugee Problems in Africa, those recognized in accordance with the UNHCR statute, individuals granted complementary forms of protection, and those enjoying temporary protection. The refugee population also includes persons in refugee-like situations."
Asylum-seekers (with ‘pending cases’): "iIndividuals who have sought international protection and whose claims for refugee status have not yet been determined. Those covered in this report refer to claimants whose individual applications were pending at the end of 2014, irrespective of when those claims may have been lodged."
Internally Displaced Persons (IDPs): a"Persons or groups of persons who have been forced to leave their homes or places of habitual residence, in particular as a result of, or in order to avoid the effects of armed conflict, situations of generalized violence, violations of human rights, or natural or man-made disasters, and who have not crossed an international border. For the purposes of UNHCR’s statistics, this population only includes conflict-generated IDPs to whom the office extends protection and/or assistance. The IDP population also includes persons in an IDP-like situation."
Returned IDPs: "IDPs who were beneficiaries of UNHCr’s protection and assistance activities, and who returned to their area of origin or habitual residence between January and December 2014. In practice, however, operations may assist IDP returnees for longer periods."
Returned Refugees (returnees): "Former refugees who have returned to their country of origin, either spontaneously or in an organized fashion, but are yet to be fully integrated. Such returns would normally take place only under conditions of safety and dignity. for the purposes of this report, only refugees who returned between January and December 2014
are included, though in practice operations may assist returnees for longer periods".
Persons Under UNHCR’s Statelessness Mandate: "Defined under international law as those not considered as nationals by any state under the operation of its law. in other words, they do not possess the nationality of any state. UNHCR statistics refer to persons who fall under the agency’s statelessness mandate as those who are stateless according to this international definition, but data from some countries may also include persons with undetermined nationality. UNHCR has been given a global mandate by the united nations General Assembly to contribute to the prevention and reduction of statelessness and the protection of stateless persons. The agency also performs a specific function, under Article 11 of the 1961 Convention on the reduction of statelessness, in receiving claims from persons who may benefit from the statelessness safeguards contained in that Convention, and in assisting them and the states concerned to resolve these claims. Other groups or persons of concern refers to individuals who do not necessarily fall directly into any of these groups but to whom UNHCR has extended its protection and/or assistance services, based on humanitarian or other special grounds".