Synchronous / Asynchronous

Whether we are talking about communication, training or tools, synchronous describes something that happens in real time and expects an immediate response. Conversely, asynchronous describes something that comes from intermittent, non-continuous exchange.

A few examples make the definition simpler:
- Asynchronous communication: emails and text messages. You send a question to someone, who can answer immediately or much later. We don't necessarily expect an instant response: we don't need to wait for one before sending another email or text.
- Synchronous communication: video calls, phone exchanges, in-person or remote meetings. It is a direct, real-time exchange between participants. You can't (although some manage to remotely) carry out several conversations simultaneously.

Special case: instant messaging tools (Slack, WhatsApp, Messenger…) whose name and interface might suggest synchronous communication are in fact asynchronous.
A WhatsApp message is really just like an email or a text, dressed up in an interface that feels real-time.

More examples:
- Synchronous training: « classic » classroom training, on site or via a video call, is synchronous. Everyone gets the same information at the same time, and participants can interact with one another in real time.
- Asynchronous training: online training where content is downloadable or available on demand. The teacher/trainer creates the material in advance and makes it available to learners, who go through it at their own pace. There are no live exchanges between participants — except, perhaps, on forums… which is, of course, asynchronous communication :)