This is the 13027th most frequent Spanish word.
planas
"Planas" means "flat" or "level" in English.
Here, 'planas' describes the physical characteristic of 'hojas de papel' (sheets of paper) being flat, using it as an adjective.
Las hojas de papel son planas.
The sheets of paper are flat.
In this sentence, 'planas' refers to written exercises for practice, commonly used in the context of learning and school.
Las planas que escribiste en el cuaderno son muy ordenadas.
The exercises you wrote in the notebook are very neat.
Here, 'planas' describes the attribute of 'superficies' (surfaces) being flat, functioning as an adjective.