The most common technical terms, explained briefly and in plain English, so every line of a quote or an operations discussion is easy to follow.
VPS
Virtual Private Server: an isolated virtual machine carved out of a physical server, with its own operating system and guaranteed resources.
KVM
Linux's built-in virtualisation technology. It gives strong isolation between instances, which is why a KVM-based VPS is worth choosing over older, less well-isolated solutions.
vCPU
A processor core allocated to the virtual machine. It matters whether the capacity is guaranteed or just shared, the difference shows up at peak times.
LTS
Long Term Support: an Ubuntu release with long-term support and five years of standard security patches. A production server always runs LTS, never an interim release.
Hardening
Security hardening: turning off unnecessary services, tightening permissions, restricting access methods. Part of the setup, not an afterthought.
SSH key
Access via a cryptographic key pair instead of a password. It can't be guessed and can't be brute-forced, which is why we turn off password-based SSH login.
Firewall (UFW)
Only lets through the ports that are actually needed. Everything is denied by default, and only the necessary services get an exception.
Fail2Ban
Watches the logs and automatically bans IP addresses that repeatedly fail to log in. This puts a stop to the bot attacks flooding the logs.
Reverse proxy
A server placed between the visitor and the application (typically Nginx) that handles encryption, compression and traffic distribution.
Varnish
A full-page cache in front of the web server. Most visitors get a ready, stored page, so PHP and the database never even get loaded.
Redis and Valkey
In-memory caches for sessions and object caching. Valkey is the open-source continuation fork of Redis.
PHP-FPM pool
An isolated group of PHP processes. A separate pool per website means one site being overloaded or broken doesn't take the others down with it.
OPcache
Keeps PHP's precompiled code in memory, so the source doesn't need to be parsed again on every request. Free speed, when sized correctly.
Cron
The engine behind scheduled background tasks: indexing, sending email, feed generation, backups. If cron isn't running, the system appears to work, but a lot quietly stops happening.
systemd
Ubuntu's service manager. It starts and keeps background processes alive, and restarts them if they stop unexpectedly.
RPO
Recovery Point Objective: how much data we're willing to lose in the worst case. With one backup a day, that's at most a day's work.
RTO
Recovery Time Objective: how long it takes for the system to come back after a serious failure. With large amounts of data this can run into hours, and it's worth knowing in advance.
Snapshot
A snapshot of the entire virtual machine. Good for a quick rollback, but it doesn't replace a versioned backup kept on separate storage.
SPF, DKIM, DMARC
Three DNS-based email authentication standards. Together they ensure that mail sent in your name counts as authentic and doesn't end up in spam.
TTL
The lifetime of a DNS record. Lowered before a server migration, the switch propagates in minutes instead of hours.
Uptime
The proportion of time a service is available. 99.9% means about 43 minutes of downtime a month, it's worth thinking in numbers, not adjectives.
Load average
A measure of system load. On its own it doesn't say much, it's meaningful relative to the number of cores, and that's when you find out if capacity is tight.
Staging
A copy of the live system where updates and development can be tried out beforehand. Anyone who tests directly in production is really testing on their customers.
WAF
Web application firewall that filters incoming requests against known attack patterns. A good extra layer of protection, but it doesn't replace updates.