Planets are contra-parallel when they are have the same Declination, and both are in opposite hemispheres, one north and one south of the equator. They could be anywhere in the zodiac, with or without a longitudinal aspect, but will be contra-parallel when they are the same number of degrees from the equator but with one on the north side and the other on the south side.
Since planets in an opposition aspect are often also contra-parallel, these declination aspects are often interpretted like being in opposition, regardless if they are opposite in the zodiac. Or they may be interpretted as being simply a balancing resonance or energy. The opposition aspect is based on planets being in signs that are opposite each other in the zodiac, whereas contra-parallel planets could theoretically be in any pair of signs.
Glyph: or -//-