can anyone show me what it is?? or what does it do??

i've a pict here.. if you can circled it.. that'll be great..
erm.. i got a quotation to replaced it.. it cost like $180.. was wondering if anyone have an experience with this?? there's this noise from the back of my car (like a lil thump) everytime i step on the brakes.. i brought my car into a shop.. they told me its my caliper bushing.. so i need some info from you guys coz i've no idea what it is and what it does?? thanks in advance..

i've a pict here.. if you can circled it.. that'll be great..
erm.. i got a quotation to replaced it.. it cost like $180.. was wondering if anyone have an experience with this?? there's this noise from the back of my car (like a lil thump) everytime i step on the brakes.. i brought my car into a shop.. they told me its my caliper bushing.. so i need some info from you guys coz i've no idea what it is and what it does?? thanks in advance..