From 2015 to 2017, UrbanToronto and its sister publication, SkyriseCities, ran an occasional series of articles under the heading Explainer. Each one took a concept from Urban Planning, Architecture, Construction, or other topics that often wind up in our publications, and presented an in depth look at it. It's time to revisit (and update where necessary) those articles for readers who are unfamiliar with them. While you may already know what some of these terms mean, others may be new to you. We will be (re)publishing Explainer on a weekly basis.