Buck-Boost Converters are power supplies that are 'ambidextrous' - they can convert lower or higher voltages to one steady output. A good idea for if, say, you have something that could be powered by USB or two AA's but you want 3.3V output. Much like the name implies, they can both 'buck' the voltage down, and 'boost' the voltage up.

For our Toy Hacker board, let's try to find a low cost buck-boost chip that will give us about 500mA of 3.3V output even from two nearly-dead AA batteries that are 0.9V. We want something somewhat small and fairly inexpensive, efficiency isn't the most important since we expect folks to use rechargeable AAs anyhow.

See the chosen part on DigiKey https://www.digikey.com/short/jhdzw3r5