From BiblePortal Wikipedia

Hastings' Dictionary of the Bible [1]

Eglath-Shelishiyah occurs in an ancient oracle against Moab, which is quoted in   Isaiah 15:5 and   Jeremiah 48:34 . In both these passages RV [Note: Revised Version.] takes the word to be a proper name, giving in margin the alternative tr. [Note: translate or translation.] ‘[as] an heifer of three years old,’ which is AV [Note: Authorized Version.] in   Jeremiah 48:34 and AVm [Note: Authorized Version margin.] in   Isaiah 15:5 . In the latter passage, AV [Note: Authorized Version.] text omits ‘[as].’ It is still somewhat uncertain whether the word is an appellative or a proper name, although the latter view has commended itself to the majority of modern scholars.

Holman Bible Dictionary [2]

 Isaiah 15:5 Jeremiah 48:34

Maxwell Miller

International Standard Bible Encyclopedia [3]

eg´lath - shel - i - shı̄´ya ( עגלת שׁלשׁיּה , ‛eghlath shelı̄shı̄yāh ): Found in  Isaiah 15:5;  Jeremiah 48:34 (Hebrew) in oracles against Moab. the King James Version translates "an heifer of three years old"; the Revised Version (British and American) takes it as the name of a place, but the American Revised Version, margin has "a heifer three years old," according to Septuagint. In the former case strong and unconquered cities, Zoar and Horonaim, are compared to the heifer not yet broken to the yoke. Such use of "heifer" is not infrequent (compare   Jeremiah 46:20;  Hosea 10:11 , etc.). The majority of scholars, however, take it as a place-name. Some would read "the third Eglath," as if there were three towns of that name. No probable identification has been suggested.