With the derived property of type Combine, it is possible to combine values from different properties. Go to Catalog > Derived Properties and create a new derived property of type Combine.

Suppose you want to create a filter for gender, but this is based on two feeds properties. With the derived property of type Combine, you can then combine them into one property. As shown in the example below: 

In the Value column you can specify which value you want to use, for example, this could be the filter value you want to show in your filter.
In the OR/EN column you choose whether it should satisfy multiple properties or just one of the entered properties. In the example above you see AND, this means that a product gets the value 'Ladies' if it has both Age Group=Adult and Sexe=Ladies.
In the Property column choose the property you want to use. 
In the Operator column choose how you want to determine the value. You can choose from: equal to, not equal to, starts with, does not start with, ends with, does not end with, contains and does not contain. 
In the last Value column, you then choose the value from the property. 

Explanation Operators:

In the case of equal to and not equal to, you can choose one of the values of the selected property from the dropdown. If you choose starts with, does not start with, ends with, does not end with, contains and does not contain then you can still fill in the value yourself. For example, if you want to use a word from the description of a product as a property you can do this with contains, like the example below: