Researches are performed in the Academy and are for various things to help improve your city
Here is a list of the different Researches:
Agriculture
Lumbering
Masonry
Mining
Metal Casting
Informatics
Military Science
Military Tradition
Iron Working
Logistics
Compass
Horseback Riding
Archery
Stockpile
Medicine Construction
Engineering
Machinery
Privateering
here is a chart of the researches' requirements [1]