A phonorecord is defined by the United States Copyright Act of 1976 to be a material object which embodies sounds (other than those accompanying audio-visual recordings such as movies), for example cassette tapes, CDs or albums.
To explain the difference, a person or group takes a song and makes a performance. That performance is a sound recording (also called phonogram); the physical media that the sound recording is stored upon is a phonorecord.
All of the following are "phonorecords" under the law: A wire recording; a 16-rpm, 33-rpm, 45-rpm or 78-rpm phonograph record (vinyl disc), a reel-to-reel tape, an 8-track tape, a compact cassette tape, a compact disc, an audio DVD, and an MP3 file stored on a computer, compact disc or USB flash drive.
From the Copyright Act: “Phonorecords” are material objects in which sounds, other than those accompanying a motion picture or other audiovisual work, are fixed by any method now known or later developed, and from which the sounds can be perceived, reproduced, or otherwise communicated, either directly or with the aid of a machine or device. The term “phonorecords” includes the material object in which the sounds are first fixed.