A:Error/bug/defect/mistake-->  are human intraction which produce an incorrect result.
Fault--> Fault is a stage of software which is caused by an error/bug/defect/mistake.
Failure--> It is a deviation of software from its expected delivery or service.
For eg:you are driving a car and you are on road while on driving now there is two way on the road

1) left--> mumbai

2) right--> delhi
now you have to go to delhi it means you have to turn the stearing to the right, but by mistake you turn the stearing to the left, from that position that is called as "Error" because human intraction is there. and now Fault is there till you will not reach the mumbai, but when you reach mumbai that is a final stage which is called "Failure" becoz you had to reach delhi but now you are in Mumbai.