typedef std::deque<Work_Condition_tag*> Work_Condition_List;

This line of code declares a typedef for a deque container that holds pointers to objects of type "Work_Condition_tag". The new type is called "Work_Condition_List".

A deque is a container that provides constant time insertions and deletions at both its beginning and end. It is similar to a vector in that it is a sequence container, but it allows efficient insertions and deletions at both ends.

The asterisk (*) in "Work_Condition_tag*" indicates that the deque holds pointers to Work_Condition_tag objects, rather than the objects themselves. This allows the deque to hold objects of varying sizes and avoid copying large objects when adding or removing elements.

Overall, this line of code defines a new type that will be used to store a list of pointers to Work_Condition_tag objects using a deque container.