The cURL means client URL. It allows you to connect with other URLs and use their responses in your code. You can use Curl to make all kinds of HTTP requests, including sending custom headers, sending body data, and using different verbs to make your request.
If you need to display some HTML code on the browser, first you need to convert it into HTML entities. Otherwise, the code will be processed by the PHP. For example, instead of <bold> output, the text itself will become bold.
The filter_var() function filters a variable with the specified filter. There are two types of filters: