'jar' can mean may things according to freedictionary.com jar 1 (jär) n. 1. A cylindrical glass or earthenware vessel with a wide mouth and usually no handles. 2. The amount that a jar can hold. 3. Chiefly British A glass of beer. tr.v. jarred, jar·ring, jars To put into a jar. [Middle English jarre, a liquid measure, from Old French (from Provençal jarra) and from Medieval Latin jarra, both from Arabic jarra, earthen jar, from jarra, to draw, pull; see grr in Semitic roots.] jarful n. jar 2 (jär) v. jarred, jar·ring, jars v.intr. 1. To make or utter a harsh sound. 2. To be disturbing or irritating; grate: The incessant talking jarred on my nerves. 3. To shake or shiver from impact. 4. To clash or conflict: "We ourselves . . . often jar with the landscape" (Isak Dinesen). v.tr. 1. To bump or cause to move or shake from impact. 2. To startle or unsettle; shock. n. 1. A jolt; a shock. See Synonyms at collision. 2. Harsh or grating sound; discord.

The word jar refers to a glass container with a lid. Usually food products with high acidity are put in a glass jar. However, in todays plastic world, almost all "jars" are plastic.

Yesterday I bought a jar of jam.

I 'learned' a new word "jar". How do you 'normally' use it. The 2 most common uses are to refer to a container or to refer to something that clashes with something else. In my homeland of Northern England however we do say that we are going 'out on the evening for a few jars', to mean that we will be drinking some beer.