Sardines, or pilchards, are several types of small, oily fish

Oily fish

Oily fish have oil in their tissues and in the belly cavity around the gut. Their fillets contain up to 30 percent oil, although this figure varies both within and between species...

 related to herring

Herring

Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...

s, family Clupeidae

Clupeidae

Clupeidae is the family of the herrings, shads, sardines, hilsa and menhadens. It includes many of the most important food fishes in the world.-Description and biology:...

. Sardines are named after the Mediterranean island of Sardinia

Sardinia

Sardinia is the second-largest island in the Mediterranean Sea . It is an autonomous region of Italy, and the nearest land masses are the French island of Corsica, the Italian Peninsula, Sicily, Tunisia and the Spanish Balearic Islands.The name Sardinia is from the pre-Roman noun *sard[],...

, around which they 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

Sea Fish Industry Authority

The Sea Fish Industry Authority is a United Kingdom non-departmental public body, established in 1981, and charged with working with the UK seafood industry to promote good quality, sustainable seafood. Seafish revised its mission in 2008...

, for example, classifies sardines as young pilchards. One criterion suggests fish shorter in length than 6 inches (15.2 cm) are sardines, and larger ones pilchards.