rocky ground: land where a shelf of solid bedrock lies just beneath a thin skin of soil
The word describes a very specific kind of ground, the kind that covers wide stretches of Galilee and Judea: a layer of solid rock sitting close to the surface, with only a thin coat of soil on top. It is built from the ordinary word for bedrock (πέτρα), the massive rock ledge itself, not from the word for a loose stone you could pick up and throw (λίθος). That single fact is the key to the word. It does not mean soil with stones scattered through it. It means soil with rock underneath it.
That difference is the whole engine of the one story where the word appears, the Parable of the Sower. Seed that lands on this ground springs up faster than anywhere else, because the rock just below warms the shallow soil like a hot plate and pushes the seed up quickly. Then the same shallowness kills it: the roots reach down for water, hit stone, and can go no further, so when the sun comes the plant withers as fast as it rose. The point is not that something bad (stones) was present, but that something necessary (depth) was absent.
In the tellings of the parable and in Jesus' own explanation of it, this ground stands for a certain kind of listener: someone who receives the message with instant joy but has no root, and falls away the moment trouble or pressure comes. The word keeps its plain meaning of rocky ground throughout; the parable is what gives that ground its human sense.