You've probably been in situations where someone is speaking and they seem to only focus on general ideas and concepts. They are not specific and you find it hard to relate the points to the real world. This is because their communication is more abstract.
The opposite may be even more prevalent. In this example, the person speaking is focused on very specific data points and examples. The data are interesting, but you find it hard to see the big picture. This communication is more concrete.
The best communicators are able to use both these ideas in tandem: a balance of abstract and concrete. You can think about this spectrum as a ladder: the ladder of abstraction. Samuel Ichiye Hayakawa developed this idea in 1939 in his book Language in Thought and Action.
When planning a presentation or classroom lesson, you can use the ladder to consider your points. You might ask yourself: Am I being too abstract? If so, move down the ladder to more concrete examples.