HMI stands for Interactions Human-Machine 
It's a field of research and practices a part of informatics 
but interfacing with other fields such as cognitive science, ergonomics, design, electronics, and other subjects.  
The field of HMI has two main positions. 
The first axes are to design, observe, analyze and assess the interaction and the experience human have with technologies.      
The second one is a more technological one.  
It's to design existing and future technologies and interactive environments 
we will also look at the evolution of technologies in relation to their interaction with human beings
which  will create new needs that will lead to the creation of new technologies themes 
For example, we now all have smartphones connected to the Web. 
Today's youth is always on social networks, that's something our parents could never have imagined  
Always being on social networks will create new technological requirements, resulting in more portable devices. as well as smaller technologies such as smartwatches or electronic bracelets 
This issue also brings new research questions, for example how to interact with a PC that has no screen at all.  
HMI was created in the 80s since that, it was used only by professionals who worked in the IT field.
The field of cognitive science was also created in the 70s 
it stemmed from other scientific fields such as cognitive psychology, artificial intelligence, linguistics, and philosophy 
When IT needed answers to better understand human beings, cognitive science brought those answers. 
At that time, in professional fields such as aviation and manufacturing, they concentrated on the human factor. 
Interaction between human beings and technology is beginning to be assessed. 
At that same time, they realized software development is becoming more complex. because users should be taken into account when designing IT systems. 
A more iterative conception centered on human beings is studied. That was the start of HMI Since, the field has expanded.
Today, it encompasses a wide range of areas such as data visualization, IT accessibility for disabled people, collaborative systems (direct or via a computer on the Internet), ubiquitous systems, and design processes.
The usage is a crucial concept with man-machine interaction. 
Initially, it was said that a system can be used if it was simple to learn and use. but after, this concept was widened.    
There are several ISO norms today that define the usage for example, the ISO 9241-2010 norm.  
This norm states that usage is the level according to which a product can be used by identified users to reach defined goals efficiently and satisfactorily in a particular usage context."
This definition is rather complex to understand. We'll break it down and look at the concepts separately.  
Efficiency involves precision and the degree of achievement according to which the user has reached specific goals.   
What does that mean? 
A system is effective if it allows a user to do tasks they want to do.

Then, efficiency is the relation between the resources spent, the precision, and the degree of achievement according to which the user reaches specific goals   
 More precisely, what does it mean?
A quick-to-use system that doesn't require many interactions will be more efficient than a system where the user spends a lot of time to reach their goals. 

Finally, the satisfaction 
shows positive attitudes toward the use of a product. 
does the user enjoy using it?
So that a product is usable, it has to be effective, efficient, and satisfactory. 
This is essential because even a very good algorithm that is very performant won't be used  
 if the interface with the algorithm is designed in a way it can't be used.