What does 'por nada' mean in English?

The Portuguese and Spanish phrase 'por nada' means the following in English: for nothing; or over nothing. The first equivalent is used in the example of buying something for almost nothing: comprar algo por nada. The second equivalent is used in the example of fighting or crying over the slightest thing: discutir por nada; and llorar por nada.

francis says:

there is also another extra meaning for the frase "por nada" mainly use in Mexico, which means "it's nothing", normally as an answer for a "thank you" expression. So when you say "thank you" to some one, almost always they will respond "por nada" = "it's nothing".