All jewellery wire has a tension associated with it.  This basically refers to how easily the jewellery wire bends.  When jewellery wire is made, they can run it through different processes, so that some wire bends, or is “softer” than other wire.  This “softness” is referred to as tension. 

The most common references to tension are:-

Hard (also called Full Hard) – very hard to bend.  Tends to spring back when it is bent, so you have to bend it past the point you want, and let it spring back to where you really want it to sit.  This wire, I find, is very hard to work with and is usually only found in the lower gauges.  Abbreviated to FH.

Half Hard – Is pliable, but does hold its shape.  It is very good for catches that need a lot of strength.  Like Hard wire, it does tend to spring back slightly when you bend it.  It is also good to use with shapes you want to make out of jewellery wire that do not require a lot of bending, but may need to hold the weight of a drop etc.  Abbreviated to HH or 1/2 H.

3/4 Hard - This  is still pliable, but a little harder to work with than HH.  I have only seen this used in reference to sterling siliver wire.  It is usually used for head pins, eye pins and for other findings.

Soft (also called Dead Soft) – Is very pliable.  It is very good to use with a jig or wire wrapping.  It will hold its shape but if too much weight or force is applied, it may bend out of shape. Abbreviated to DS.

So when you see jewellery wire advertised as:-

You know that this is 18 gauge gold filled wire, that is 14k quality, half hard in a round shape, and 5 feet in length!

If no tension is mentioned, then assume that it is Soft, this seems to be the standard that most people use.  However you are always best to check with the seller to confirm it.

One last note.  Sterling silver wire is a lot softer than gold filled wire.  So keep this in mind when swapping between the two - makes for a little extra fun :-)