For: everyone
The words you meet in Element and in the portal, explained in one or two sentences each. For the big picture, read Matrix in plain words.
Bridge A connection that brings chats from another service (WhatsApp, Signal, Telegram and others) into Element. Each person links their own accounts. All bridges are included in your plan.
Direct message (DM) A private chat between you and one other person.
Element The chat app you use with your server. It runs in the browser (Element Web) and on the computer (Element Desktop).
Element X The Element app for iPhone and Android.
End-to-end encryption Messages are locked on your device and unlocked only on the devices of the people in the chat. Nobody in between can read them, not even MatrixHost. It is on by default in direct messages and private rooms.
Federation
Matrix servers can talk to each other, like email providers. That's why you can invite someone from another Matrix server, for example @anna:matrix.org.
Matrix The open standard behind your chat, like the rules that make email work between providers.
Matrix ID (user ID)
Your full chat address, for example @marco:8e43f5db6a.matrixhost.eu: your username, then your server.
Portal The MatrixHost website at matrixhost.eu, where the account owner manages users, passwords, billing and backups. Its login (your email address) is separate from your chat login.
Recovery key A long code Element gives you at your first sign-in. It is the spare key to your encrypted messages: you need it on a new device if no other device is at hand. Store it safely. We cannot recover it.
Room A chat with one or more people, for example "Team" or "Sales". Rooms can be private (invite only) or open to everyone on your server.
Server (homeserver)
Your company's own chat server, for example 8e43f5db6a.matrixhost.eu. "Homeserver" is the technical name you may see in Element.
Session (device) Each place where you are signed in: a browser, a computer, a phone. Each one is a separate session.
Space A group of rooms, like a folder, for example one space per department.
Username
The first part of your Matrix ID, for example marco. You use it to sign in, not your email address.
Verification Confirming that a new device really belongs to you, by comparing emoji or scanning a QR code with a device where you are already signed in, or by entering your recovery key. After that, the new device can read your encrypted messages.