Virtual Network Computing (VNC) is a system that provides remote computer connection. All your mouse movements and keys pressed are transfering to your server as well as display. It's all the same as remote desktop.
SSH — network protocol which allows to manage an OS remotely and create TCP tunnels (e.g. for file transfer). Whole SSH traffic including transferred passwords is encrypted. Very useful as remote terminal as well as remote program starter: VPN, IRC, PROXY etc.
Hot Spare is a technology for electronic hardware backup, where reserve hardware is connected to the system replaces a broken component automatically, or at least excepting system work interruptions. Hot Spare most often used for Server SSD and RAM.
RAID50 array where each one of them is a full copy of another one. Provides good write speed and advantages of reading speed on a request parallelization. High reliable — works until at leas one disk from the array functions. Risk of breakage of two disks at the same time is minimal.
Tier 1 — internet access via peer connections only. This is the best broadband to the internet today. Network uptime 99.99%.
