Brake Fluid Leak

I've got a '99 Disco and it began to lose all of it's brake fluid the other day. I thought it could be the lines, so a bit more fluid was added and it all appears to be leaking from the black rubber bit that's behind the pad, where the line goes into the wheel. What is this part called? How do I fix this?
Thank you.

it's called a brake caliper and i'm not being funny but if you don't know that then let a mechanic sort it. brakes ain't for beginners, end o the day, if you botch it you could kill someone...

take it along to your local repair shop, and get them to fix it, as said brakes are not a thing to be trifled with if you do not know what you are doing,

I should say so to!!! its most likely the seal for the piston thats gone and is NOT a job for begginers .