It can be compared with asynchronous learning, where learner and teacher may not be in the same place at the same time. Both terms are often used when talking about online learning.
Example
In online learning, videoconferencing, chat and VOIP are synchronous learning tools because the learner and teacher interact in real time.
In the classroom
Synchronous learning tools are often expensive, difficult to set up and limited by technological constraints. It is a good idea to have an alternative lesson planned or to incorporate synchronous learning as a stage rather than as an entire lesson, for example using chat as a pre-lesson activity or videoconferencing as the final event in a project.
Further links:
https://www.teachingenglish.org.uk/article/motivation-e-learning-personal-reflections
https://www.teachingenglish.org.uk/blogs/nikpeachey/10-tasks-training-teachers-use-web-20-tools
https://www.teachingenglish.org.uk/blogs/neilballantyne/online-learning-teacher-training