How can I understand this binary expression grammar?

Question

I don't understand this binary expression grammar

expr -> expr '+' term
      | expr '-' term
      | term

term -> term '*' factor
      | term '/' factor
      | factor

factor -> '(' expr ')'
        | NUM 

Answer 1

In plain english:

An expr can be one of the following:

• another expr followed by the character + followed by a term
• another expr followed by the character - followed by a term
• a term

A term can be one of the following:

• another term followed by the character * followed by a factor
• another term followed by the character / followed by a factor
• a factor

A factor can be one of the following:

• a character ( followed by and expr followed by a character )
• a number