if a piece of writing, set of ideas etc is coherent, it is easy to understand because it is clear and reasonable:
The three years of the course are planned as a coherent whole.
a coherent account of the incident
if someone is coherent, they are talking in a way that is clear and easy to understand:
He sounded coherent, but he was too ill to have any idea what he was saying.
if a group is coherent, its members are connected or united because they share common aims, qualities, or beliefs:
They were never a coherent group.
She could not think coherently.