I had previously written a post related to coupling and cohesion here and that was more of a basic definition of both the terms.
In this post I would like to throw some light on the tight dependency on the type of the component in use. Generally we would aim to design classes such that they interact via the interfaces or more generally put via API. Suppose we use interfaces (more of a generic term where we dont have implementations, not specific to keyword interface in Java or C#), but this is not enough, we need to provide some kind of implementation for the interface which is actually consumed by the other client classes.