To steam is to suspend food over simmering liquid, usually water, so the ingredients cook as the hot vapor swirls around them. A variety of tools can be employed to create this culinary sauna, some designed for the task, others improvised. In the West, there's the metal steamer insert fitted into a pot. In the East, the multilevel bamboo steamer is the gear of choice, enabling cooks to stack ingredients in tiers. The French often wrap foods en papillote, in parchment paper, thus steaming them in their own juices.
Regardless of how you choose to harness steam, a tight seal is essential. Monitoring the water level is also important. Too much water, and food is immersed-boiling, not steaming. Too little, and you risk evaporation and scorched pans; in this case, any water you add should be boiling hot. Steaming is a friend to harried cooks (it's speedier than waiting for a whole stockpot of water to boil) and, with the right ingredients, to health-minded ones (you can often forgo additional cooking fats). The method also can preserve nutrients and color, and impart the subtle flavors of broth, wine, or herb-infused liquids. Just some of the great reasons to go full steam ahead.