It helps vent steam out of your pie while it bakes. (thevegankat.com)
It has a glass lid, which helps you monitor different types of rice as they cook without venting steam. (geekwrapped.com)
The TEPCO operators of the stricken nuclear power plant — a minimal staff of 50 as all non-essential personnel have been evacuated — now face a balance between venting the steam building up in the reactor (since the main danger for a widespread release of radioactive material is steam bursting the thick steel container holding the reactor) and keeping any radioactive materials inside the power plant itself. (scientificamerican.com)