Define a context free grammar. What are the applications of context free languages?

Context free grammar (CFG): A contest free grammar is a finite set of variables each of which represents a language. A context free grammar (CFG) is denoted
G = (V, T, P, S)
Where,
V = a finite set of variables
T = a finite set of terminals
P = a finite sets of production or rules that represent the recursive definition
Of a language. Each production consists of: 

• A variable that is being defined by the production. 
• The production symbol. 
• A string of zero or more terminals and variables. 

So that it is of the form A → α, where A is a variable and α is a string of symbols from (V ∪T).
S = is a special variable called the start symbol
Of a language. Each production consists of: 

• A variable that is being defined by the production. 
• The production symbol. 
• A string of zero or more terminals and variables. 

So that it is of the form A → α, where A is a variable and α is a string of symbols from (V∪T).
The applications of context free languages: 
(i) In an early application, grammars are used to describe the structure of programming languages.
(ii) In a newer application, they are used in an essential part of the Extensible Markup Language (XML) called the Document.
(iii) In most programming languages opening and closing of braces, a curly bracket is taken care. It mainly tracks it and if any closing bracket is not there, it will throw error.