has type is a special property in Semantic MediaWiki with a built-in meaning: it assigns a type to a property. For example, the page for property Population would specify [[has type::Number]]. Has type assumes its value is in the Type namespace, so you can omit Type:.
Note that you can't perform a semantic search for articles with this special property. Instead, use the special Properties page which gives the type of each property in use; or the special "All Pages" page to display all articles in the Property namespace.
SMW 1.0 allows N-ary relations, where a property can take multiple values. You express this by listing multiple types as the value of Has type, separated by semicolons. For example, on ontoworld.org ow:Property:Employment takes a link to a company, a job title, and a start and end date, so it specifies its type as [[has type:=Page; String; Date; Date]].