I see in some courses that some people highlight something like a middleware, example : middleware, authentication ). I found the explanation rather superficial because it was not the focus of the course, I did not really understand what middleware is.
Well, we can answer these two questions together: a middleware is, in very simple terms a layer in the middle that is, a layer that helps two applications, parts, systems, communicate.
It serves to make communication easier or viable. We think of interfaces, convert data and formats, provide protocols, among others.
It then serves to provide or facilitate communication between two applications, which can come from different platforms and different technologies.
An interesting image that illustrates this is this:
Source: Is-an-API-considered-middleware
Interesting in this image is that it shows an API as a middleware , that is, it provides an intermediate layer for communication, for example between a company service and an external user.
You see, here's just illustrating, as an example, an API running as a middleware , but both are distinct things.
There is no clear definition of what types of middleware I have read about, and each source has a definition. Not thinking of types but where these types of applications are most common, we could list:
