An entablature is that portion of a building between the capitals of the columns and the roof, including in classical architecture the architrave, frieze, cornice and pediment.
The architrave is the lintel, or lowest section of the entablature that rests directly upon the capitals of columns.
The frieze is the middle part of the entablature between the architrave and the cornice, usually decorated but may be plain.
The cornice is the top, projecting portion of an entablature. Also, any horizontal architectural member projecting from the top of a wall.
A pediment is the triangular space or gable at the end of a building, formed in the entablature by the sloping roof and the cornice.
Note: The above descriptions are based on definitions in The Penguin Dictionary of Architecture (Fourth Edition) and Arts & Ideas (Eighth Edition).
Credits: Photo, Wikimedia Commons; Illustration, The Penguin Dictionary of Architecture (Fourth Edition).