In trisomy, there is an extra copy of ONE chromosome in an egg or sperm cell. As a result, after fertilization the fetus has 47 chromosomes instead of the usual 46. An example of this is Downs Syndrome, in which there is an extra chromosome 21.
In triploidy, the fetus has an entire extra set of chromosomes -- so it has 69 chromosomes instead of the usual 46. A triploid fetus almost always results in miscarriage or stillbirth. There is too much genetic material for the baby to survive. If it is born, it dies in infancy.
Somatic (body) cells of organisms that reproduce sexually normally contain two copies of each chromosome--one from the mother and one from the father. When gametes are being formed, the number is cut in half, so that each parent contributes one copy, and the offspring has, again, two copies.
In triploidy, all body cells have received one copy of the all chromosomes from one parent, but BOTH copies from the other. These organisms usually do not survive.
In trisomy, the offspring receives a double copy of just one of the chromosomes. Depending on which chromosome is involved, different conditions result; Down Syndrome is one of the most well-known examples.
Triplody occurs when you've got an entire third set of chromosomes. (The fetus would have 69, rather than the standard 46 chromosomes.) This so devastating that it often produces miscarriages.
Trisomy happens when you get a specific chromosome multiplied, so there are three instead of two. This produces specific abnormalities depending on which chromosome is tripled.
Trisomy is the situation in which there are three copies of the particular chromosome.
Triplodiy is the presence of three homologous sets of chromosomes.