When you're beginning a research project or intense study in an area that's new to you, it's often a good idea to do some background reading and vocabulary building, before you delve into the professional literature. Reference books can be excellent places to start your reading.
Aesthetics A-Z by Eran Guter
The Bloomsbury Guide to Art edited by Shearer West
Critical Terms for Art History edited by Robert S. Nelson and Richard Shiff
Encyclopedia of American Folk Art edited by Gerard C. Wertkin and Lee Kogan
The Grove Encyclopedia of Materials and Techniques in Art edited by Gerald Ward
The Thames & Hudson Dictionary of Art and Artists edited by Edward Read and Nikos Stangos
The Thames & Hudson Dictionary of Design Since 1900 by Guy Julier
The Thames & Hudson Dictionary of Graphic Design and Designers by Alan and Isabella Livingston