Error: The deviation from the required logic, syntax or standards/ethics is called as error.

There are three types of error. They are:

Syntax error (This is due to deviation from the syntax of the language what supposed to follow).

Logical error (This is due to deviation from the logic of the program what supposed to follow)

Execution error (This is generally happens when you are executing the same program, that time you get it.)

Defect: When an error found by the test engineer (testing department) then it is called defect

Bug: if the defect is agreed by the developer then it converts into bug, which has to fix by the developer or post pond to next version.