There are international agreements on the definition of POW dating back to the Lieber Code declared by Lincoln in 1862
A prisoner of war is a public enemy armed or attached to the hostile
army for active aid, who has fallen into the hands of the captor,
either fighting or wounded, on the field or in the hospital, by
individual surrender or by capitulation.
All soldiers, of whatever species of arms; all men who belong to the
rising en masse of the hostile country; all those who are attached to
the army for its efficiency and promote directly the object of the
war, except such as are hereinafter provided for; all disabled men or
officers on the field or elsewhere, if captured; all enemies who have
thrown away their arms and ask for quarter, are prisoners of war, and
as such exposed to the inconveniences as well as entitled to the
privileges of a prisoner of war.
Moreover, citizens who accompany an army for whatever purpose, such as
sutlers (sic), editors, or reporters of journals, or contractors, if
captured, may be made prisoners of war, and be detained as such.
The monarch and members of the hostile reigning family, male or
female, the chief, and chief officers of the hostile government, its
diplomatic agents, and all persons who are of particular and singular
use and benefit to the hostile army or its government, are, if
captured on belligerent ground, and if unprovided with a safe conduct
granted by the captor's government, prisoners of war.
If the people of that portion of an invaded country which is not yet
occupied by the enemy, or of the whole country, at the approach of a
hostile army, rise, under a duly authorized levy en masse to resist
the invader, they are now treated as public enemies, and, if captured,
are prisoners of war.
and through to the Geneva Convention (III) relative to the Treatment of Prisoner of War, 12 August 1949:
Art 4. A. Prisoners of war, in the sense of the present Convention,
are persons belonging to one of the following categories, who have
fallen into the power of the enemy: (1) Members of the armed forces
of a Party to the conflict, as well as members of militias or
volunteer corps forming part of such armed forces.
(2) Members of other militias and members of other volunteer corps,
including those of organized resistance movements, belonging to a
Party to the conflict and operating in or outside their own territory,
even if this territory is occupied, provided that such militias or
volunteer corps, including such organized resistance movements, fulfil
the following conditions: (a) that of being commanded by a person
responsible for his subordinates; (b) that of having a fixed
distinctive sign recognizable at a distance; (c) that of carrying
arms openly; (d) that of conducting their operations in accordance
with the laws and customs of war.
(3) Members of regular armed forces who profess allegiance to a
government or an authority not recognized by the Detaining Power.
(4) Persons who accompany the armed forces without actually being
members thereof, such as civilian members of military aircraft crews,
war correspondents, supply contractors, members of labour units or of
services responsible for the welfare of the armed forces, provided
that they have received authorization, from the armed forces which
they accompany, who shall provide them for that purpose with an
identity card similar to the annexed model.
(5) Members of crews, including masters, pilots and apprentices, of
the merchant marine and the crews of civil aircraft of the Parties to
the conflict, who do not benefit by more favourable treatment under
any other provisions of international law.
(6) Inhabitants of a non-occupied territory, who on the approach of
the enemy spontaneously take up arms to resist the invading forces,
without having had time to form themselves into regular armed units,
provided they carry arms openly and respect the laws and customs of
B. The following shall likewise be treated as prisoners of war under
the present Convention:
(1) Persons belonging, or having belonged, to
the armed forces of the occupied country, if the occupying Power
considers it necessary by reason of such allegiance to intern them,
even though it has originally liberated them while hostilities were
going on outside the territory it occupies, in particular where such
persons have made an unsuccessful attempt to rejoin the armed forces
to which they belong and which are engaged in combat, or where they
fail to comply with a summons made to them with a view to internment.
(2) The persons belonging to one of the categories enumerated in the
present Article, who have been received by neutral or non-belligerent
Powers on their territory and whom these Powers are required to intern
under international law, without prejudice to any more favourable
treatment which these Powers may choose to give and with the exception
of Articles 8, 10, 15, 30, fifth paragraph, 58-67, 92, 126 and, where
diplomatic relations exist between the Parties to the conflict and the
neutral or non-belligerent Power concerned, those Articles concerning
the Protecting Power. Where such diplomatic relations exist, the
Parties to a conflict on whom these persons depend shall be allowed to
perform towards them the functions of a Protecting Power as provided
in the present Convention, without prejudice to the functions which
these Parties normally exercise in conformity with diplomatic and
consular usage and treaties.
As there is no category in either the Lieber Code or the current Geneva Convention that would qualify the "Japanese Americans forced into concentration camps during WWII " as POW's, it is simply a gross misuse of the language to claim otherwise.