Cannot modify header information - headers already... Error [duplicate]

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• How to fix “Headers already sent” error in PHP 11 answers

Cannot modify header information - headers already sent by (output started at /home/xxxxx/public_html/wp-content/themes/xxxxxx/form.php:2) in /home/xxxxx/public_html/wp-includes/pluggable.php on line 1207.php

I got this error when i tried to run a front end form on my website. I didnt get this error in the webmatrix localhost. I got rid of this error by removing <?php get_header(); ?> in the form. Just as i removed the <?php get_header(); ?> and reloaded the form the post was submitted.

Now my question is why was i getting that error and what was the meaning of it ?

via Chebli Mohamed