Refers to the time between the browser requesting a page and when it receives the first byte of information from the server. In a nutshell, it is the period before the first byte reaches from the server to the browser. When users want to access a web page, the browser sends a request to the server on which the web page in question is located. After the server responds positively to the browser request, the user is able to display the relevant web page. The rapid arrival of the server response allows the user to quickly view the web page in question. Therefore, the amount of time that passes until the first byte is sent by the server to the browser is of critical importance.