Natural unsaturated fatty acids are in configuration that is called cis, but partial hydrogenation can flip the chemical bonds into a different configuration that is called trans. In cis configuration the chains of carbon atoms are on the same side of the double bond, resulting in a kink. In trans configuration hydrogen atoms are on the opposite side of the double bonds of the carbon chain, making the fat molecule straight.
Melting point : cis-fats usually low, some cis fats are liquid at room temperature.
trans-fats - usually high, trans fats are solid at room temperature.
Cis-fats occur naturally, the majority of trans-fats come from processed foods