“Sardine” and “pilchard” are common names for various small, oily forage fish in the herring family Clupeidae. The term “sardine” was first used in English during the early 15th century, it comes from the Italian island of Sardinia, around which sardines were once abundant.
The terms “sardine” and “pilchard” are not precise, and what is meant depends on the region. The United Kingdom’s Sea Fish Industry Authority, for example, classifies sardines as young pilchards. One criterion suggests fish shorter in length than 15 cm (6 in) are sardines, and larger fish are pilchards.
The FAO/WHO Codex standard for canned sardines cites 21 species that may be classed as sardines. FishBase, a comprehensive database of information about fish, calls at least six species “pilchard”, over a dozen just “sardine”, and many more with the two basic names qualified by various adjectives.
Info and Image from Wikipedia