Also known as big-bang reproduction. Semelparity is the biological act of putting everything you have into the act of reproduction, and then dying.
Chinook Salmon do this because the effort of getting to the top of the river, and then defending their nests, takes up all their energy. If they didn't do their best, they wouldn't be able to reproduce successfully.
Agave plants do it to compete with the other agaves, trying to have the highest flower stalk, so as to attract the most pollinators.
The Chinese Bamboo blooms once every 120 years, and then puts all of it's energy into making seeds, trying to produce enough to satisfy the appetites of all the forest predators, and then have enough left over to start another bamboo grove. After this it dies.
Semelparity is also common in insects. If you aren't going to live long, and you don't have any parenting skills, having as many kids as possible is the best way of passing on your genetic material. Using every last bit of your energy to produce young, and then perhaps letting them eat your body, giving them more energy, is just smart.
For a better explaination, read Natural Acts: Love's Martyrs by David Quammen.