IDictionary get(string ticker, string type, DateTime from, DateTime To);

Question

IDictionary<DateTime, Double> get(string ticker, string type, DateTime from, DateTime To);
is in the interface called "ITimeSeries.cs"
I have to implement that but I am just wondering what the following does.
IDictionary<DateTime, Double> get(string ticker, string type, DateTime from, DateTime To); 
I know how IDictionary works(its like hashTable) but what "get(string ticker, string type, DateTime from, DateTime To);" is for in this case? and how is it used with "IDictionary<DateTime, Double> "?
 
Thanks