What are comments in programming languages?

Sometimes when we hear a conversation or a lecture with a lot of jargon or acronyms, we may wonder if it could have been explained in simple words with more context.  Comments in a programming language serve exactly this purpose.

Programs are often difficult to read, especially ones that involve complex logic or multiple components that talk to each other. Comments help add contextual information to a piece of code. Sometimes it helps explain the rationale or a business need on why certain logical decisions were made as opposed to another.

/*A service that implements all functions related to the Employee Module in the HRisFarce Application*/

class EmployeeServiceImpl implements EmployeeService{
	@Service
	PremiumPerkService premiumPerkService;
    
    // method that discerns class structures in an organization and provides
    // perks deemed appropriate for its workforce
	List<Perks> getEmployeePerkList(Employee employee){
    	if(employee.isExecutive)
        	return premiumPerkService.getPremiumList();
        return new ArrayList<>();
    }
}

Multi-line comments v/s single line comments
Most languages follow the following syntax:

/* This is a multi
line comment*/

// This is a single comment

Some languages use # for single line comments.

# single line comment

Some conventions:

• Keep the comments as concise and reader friendly as possible. If one needs to google your comments then it defeats the purpose.
• Avoid abbreviations when possible.
• Curb the urge to over-explain your implementation. Stick to context that is relevant for the reader to understand your program. You write code, not blog posts or maybe you do both?!
• Avoid explaining names of variables or constants, their nomenclature should be self-explanatory. That is another convention you should read about.