A stock character is one that is a typical sterotype or archetype. In Twelfth Night, Maria is definitely a 'stock character' in that she is Olivia's maid in waiting, which means that they are very close. The lady in waiting, or maid in waiting, is often cast as the one that knows everything and is the glue that puts things together, or can pull them apart....and this is just the function she serves in this instance.
