SitePlus+ is one of many “Site” features of Wealthy Affiliate’s hosting platform which itself is called SiteRubix. SitePlus+ is currently composed of two different features: SiteSSL and SiteProtect.
SiteSSL is Wealthy Affiliates’s implementation of free Let’s Encrypt SSL certificates on SiteRubix. With a click of a button, Wealthy Affiliate members can install a SSL certificate on their premium website at no extra cost, provided that their website is hosted at SiteRubix(which is included in the premium Wealthy Affiliate membership.)
SiteProtect is the name Wealthy Affiliate gives its implementation of algorithms that block spam at the server level. This feature lessons the load on your website because it prevents the automated spam bots from even hitting your website.
SiteSpeed falls under the SitePlus+ umbrella as well, but I’ve written an entire post dedicated to SiteSpeed.