A frit is a ceramic composition that has been fused in a special fusing oven. They are helpful in lowering the firing temperature of a glaze.
A number of frits are available including Frit 3134 (4108). A frit from the USA, medium soft borax frit. Melts at around 620 degrees. Being low in alumina means you can add more clay in the glaze recipe helping with the suspension of the glaze.
For the full list of Frits available have a look at the pricelist.