From the Pilot/Controller Glossary:
UNCONTROLLED AIRSPACE− Airspace in which
aircraft are not subject to controlled airspace (Class
A, B, C, D, or E) separation criteria.
Also, under the heading of controlled airspace:
5. CLASS E− Generally, if the airspace is not
Class A, Class B, Class C, or Class D, and it is
controlled airspace, it is Class E airspace. Class E
airspace extends upward from either the surface or a
designated altitude to the overlying or adjacent
controlled airspace. When designated as a surface
area, the airspace will be configured to contain all
instrument procedures. Also in this class are Federal
airways, airspace beginning at either 700 or 1,200
feet AGL used to transition to/from the terminal or en
route environment, en route domestic, and offshore
airspace areas designated below 18,000 feet MSL.
Unless designated at a lower altitude, Class E
airspace begins at 14,500 MSL over the United
States, including that airspace overlying the waters
within 12 nautical miles of the coast of the 48
contiguous States and Alaska, up to, but not
including 18,000 feet MSL, and the airspace above
FL 600.
VFR charts depict where the various floors of class E airspace are.