Sausage refers to
casing stuffed with spicy meat: a tube of animal intestine or another tube-shaped casing stuffed with finely chopped pork or other meat
Sausage roll is
|sausagemeat baked in pastry: a short length of sausagemeat wrapped in pastry and baked|
Examples of any of the above are Gala, Rite, Beefy, Super Bite, Hot Dog etc.
NB: It is very wrong to refer to other brands of sausage roll as "Gala". Gala is just one of them.