Tortilla warmer. Tony Webster / flickr / 2012 / CC BY 2.0
Tortilla warmers are covered dishes used to keep tortillas warm at the table. They can keep tortillas warm for over half an hour.
They come in varying widths from 18 to 25 cm (7 to 10 inches) wide. Larger sizes can be hard to find.
They can be made of ceramic, clay or polypropylene.
Some are dishwasher safe. Sadly, though the clay ones are amongst the most decorative ones, they are of course not dishwasher safe. Given, though, that tortilla warmers are only for holding pieces of plain flour or corn flatbread, they shouldn’t need any more cleaning than a quick wipe inside, anyway.
If you want to use them for actually warming tortillas in, check before purchasing that the one you are looking at is oven safe, micro-wave safe, or both. A microwave-safe one is convenient because you can place frozen tortillas in it, zap it in the microwave without the lid on both to thaw and heat the tortillas, then place the lid on, and serve it at the table.
Substitutes
Two glass pie plates, with the second one turned upside down and acting as the lid.
Tortilla warmer interior. Glane23 / wikimedia / 2013 / CC BY-SA 3.0