SPF

   The Sender Policy Framework (SPF) is an email-authentication technique which is used to prevent spammers from sending messages on behalf of your domain. With SPF an organisation can publish authorized mail servers.

Google Tag Manager

   Google Tag Manager is a tag management system created by Google to manage JavaScript and HTML tags used for tracking and analytics on websites (variants of e-marketing tags, sometimes referred to as tracking pixels or web beacons.

Viewport - initial-scale

   The viewport is the user`s visible area of a web page. The viewport varies with the device, and will be smaller on a mobile phone than on a computer screen. Before tablets and mobile phones, web pages were designed only for computer screens, and it was common for web pages to have a static design and a fixed size.

Viewport - Width

   The viewport is the user`s visible area of a web page. The viewport varies with the device, and will be smaller on a mobile phone than on a computer screen. Before tablets and mobile phones, web pages were designed only for computer screens, and it was common for web pages to have a static design and a fixed size.

Disable Telephone link in HTML on Mobile Devices

   Telephone links are a thing. Like an anchor link you tap to (probably) go to another page, these are links you tap to call a number on a phone-capable device.

PHP 5.6.30

   PHP: Hypertext Preprocessor is a general-purpose programming language originally designed for web development.

Apache

   The Apache HTTP Server, colloquially called Apache, is free and open-source cross-platform web server software, released under the terms of Apache License 2.0. Apache is developed and maintained by an open community of developers under the auspices of the Apache Software Foundation.

Character Encoding :UTF-8

   This website is using UTF-8 character encoding in HTML , character encoding is used to represent a repertoire of characters by some kind of encoding system.

Gzip Content-Encoding

   The Content-Encoding entity header is used to compress the media-type. When present, its value indicates which encodings were applied to the entity-body. It lets the client know how to decode in order to obtain the media-type referenced by the Content-Type header.

Vary Header Accept-Encoding

   The Accept-Encoding request HTTP header advertises which content encoding, usually a compression algorithm, the client is able to understand. Using content negotiation, the server selects one of the proposals, uses it and informs the client of its choice with the Content-Encoding response header.

JSDelivr

   JSDelivr (stylized as jsDelivr) is a free public CDN for open-source projects.