These are some important qualities of good code

Cleanliness: Clean code is easy to read; this lets people 
read it with minimum effort so that they can understand it 
easily. 

Consistency: Consistent code makes it easy for people to 
understand how a program works; when reading consistent 
code; one subconsciously forms a number of assumptions and 
expectations about how the code works, so it is easier and 
safer to make modifications to it. 

Extensibility: General-purpose code is easier to reuse and 
modify than very specific code with lots of hard coded 
assumptions. When someone wants to add a new feature to a 
program, it will obviously be easier to do so if the code 
was designed to be extensible from the beginning. 

Correctness: Finally, code that is designed to be correct 
lets people spend less time worrying about bugs and more 
time enhancing the features of a program.

A code whether it is good or bad can be known only if it is 
tested. So good coding ,results in low bug density(Low 
severity +Low prioirity defects or no defects at all)

A good code which is===1. Bug free.2. 
reusable.3.independent.4.less complaxcity.5.well documented 
easy to change is called good code