What is "extra jam"?

There is a legal definition of how much fruit there must be in a preserve in order to call the produce a jam.  This definition varies from fruit to fruit.  There is a second level of fruit content above which you can call your jam, extra jam.  You can read the exciting details here on a document produced by the Food Standards Agency, with the relevant numbers starting on page 20 (annex 1, schedule 1)  

All of our jams are made with 50% fruit and 50% sugar by weight.