Glossary
The words you meet on a Mac, in plain English. For step-by-step answers, see the guides.
- Activation
- One Mac using your licence key. A licence covers 1, 5, 15 or 25 activations; you can free one to move it. More →
- AI agent session
- A running Claude Code, Codex or similar agent, with everything it started. More →
- Battery health
- How much charge your battery holds compared with when it was new. Below 80%, Apple suggests a service. More →
- Cache
- Files an app keeps to work faster next time. Safe to clear; the app rebuilds them when needed.
- Compressed memory
- Memory macOS has squeezed to make room for other apps, before it resorts to swap.
- Cycle count
- How many full charges the battery has had. Two half charges count as one cycle.
- Dev server
- A program serving a website or API on your Mac while you build it, usually on a port like 3000 or 8000. More →
- HEIC
- The photo format iPhones use: about half the size of JPG at the same quality. More →
- Helper process
- A separate process an app starts for tabs, graphics or plug-ins. Mac Health counts helpers under the app that started them.
- kernel_task
- The core of macOS. It uses CPU on purpose to slow the Mac down when it's too hot.
- Leftover
- Data left behind by an app that's no longer on your Mac. Safe to remove.
- Mbps
- Megabits per second, the unit internet speeds are quoted in. Divide by 8 for megabytes per second.
- MCP (Model Context Protocol)
- A standard way for AI assistants like Claude, Cursor and Codex to use apps and tools. OneMacTools is an MCP server; every action needs your Allow. More →
- Memory pressure
- How hard macOS is working to find memory. Green is fine; yellow and red mean apps are waiting while data is compressed or swapped to disk. More →
- node_modules
- The folder of packages a JavaScript project downloads. Recreated with npm install. More →
- Notarized
- Checked by Apple for malicious code before release, so macOS opens the app without warnings.
- OCR
- Optical character recognition: reading text in images and scans so you can search and copy it. More →
- Port
- A numbered door a program listens on for connections, like 3000 for a dev server or 5432 for Postgres.
- Responsiveness
- How quickly a connection answers while busy, in round trips a minute. What makes video calls smooth.
- Sleep assertion
- An app's request to keep the Mac or its display awake, for example during a call or a download.
- Swap
- Disk space macOS uses as extra memory when RAM runs short. Much slower than RAM.
- System Data
- The part of your Mac's storage macOS can't put in a named category: app data, caches, logs, backups, developer files and macOS's own files. More →
- Wired memory
- Memory macOS keeps for itself and can't compress or swap.