Properties may have getter and/or setter methods

Proprty getters/setters are MuranoPL methods that are invoked on attempt to get/set property value. This is required when you need to have some property access logic that is more advanced than just return/set backing field. Generally getSomething/setSomething functions can be used for that purpose but this approach has 2 disadvantages: 1) if the class had property before it cannot be converted to a function(s) without breaking compatibility with existing class users and 2) it doesn't prevent access to wraped property and thus property can be read/set bypassing corresponding functions.
Property getters/setters solve this problem by attaching those functions directly to properties.
Both getter and setter are optional. Some property types (usages) cannot have getter or setter or both. For example properties with Usage=In cannot have setters.