A mixture of presentational markup (usually HTML) and other templating code used to prepare content objects for delivery.
There are two ways templates come up in a web project. First, the term "template" is often used as an analogue to "content type," in which we identify something like a news article or accordion block as a template.
More specifically, a template provides structure around items within the content model. Multiple templates can be applied to the same object to produce different presentations. A template is normally stored as a file in a source code management system and managed as code. There will normally be at least one template per content type.