Yes. In older terms, they're referred to as "thermionic valves," as they operate on the principle of heating a plated metal item (the cathode) to emit electrons. Depending on what's in the way of the other element, the Plate, the device can be a simple one-way valve, it can amplify by modulating the electrons, or do other things like be part of an oscillator or detector (the part that takes the audio off the signal) in a radio. Most "modern" tubes have a heater, a cathode, some elements called grids, and a plate. They're called indirectly heated. Older tubes, ones designed for the battery era, just used the heater as the cathode. In modern terms, they operate more like a JFET transistor.