You'd really have to ask them... it could be something like memcached, Redis cache or simply caching files to SSD (most likely not). Frequently HostGator uses "buzz" words for their advertising/info pages. Like their unlimited stuff... nobody can really afford to give unlimited (especially file space). In fact, if I remember, they had a limit on the inodes when I was using them ages ago - and they also limited the concurrent mySQL connections to 25. If you exceeded that frequently then they "encouraged" you to go to a larger plan. I did - a VPS with another company and then shortly later dedicated servers.