Donor atoms are those impurity atoms in a semiconductor material
that give free electons to the material, for example a 5-valent
atom in a semiconductor consisting of 4-valent atoms. Acceptor
atoms are 3-valent atoms in a 4-valent semiconductor, so an
acceptor atom can "accept" an electron from the surrounding atoms
what leaves a free "hole" . Free electrons (from donor atoms) and
free holes (from acceptor atoms) make the semiconductor conduct
electricity.