Ambient computing means the devices in your environment have the capability to sense and respond to your presence and needs. This means instead of seeking out information, your devices proactively present or suggest information just when you need it. It's like a ‘digital mesh’ where devices are part of a seamless, underlying web of connections that allow free flow of data across a range of smart devices.
An example for ambient computing could be Cisco Webex that uses ultrasound emitted by meeting room hardware (such as a conference phone) to connect with computers in the same room (via their microphone) to connect the participants with the equipment seamlessly.
Another example could be Automation rules on iOS that allow you to trigger workflows based on your activity such as leaving your home, or getting out of the car.
Ambient Computing is a concept for the Internet of Things (IoT) which encompasses sensors in everyday objects that can 'talk' to one another.
With Ambient Computing the emphasis strongly lies on the personal and proactive manner in which these sensor connect through a common interface and thus allowing services to become 'smarter' by guessing what the next step is the user would request–before they request it.
For an AI-powered assistant like Digital Assistant that could mean offering a briefing about your day when it senses your on the way to the office, or setting your Out-of-Office reply automatically when you're due to be on annual leave.