Quality is delighting customers
When a defect is not identified in one phase, due to this defect more defect cause in another phase. Thus resulting increasing the number of defects. This is called defect cascading
Let me explain you with small example. Consider, you are usually collecting mobile number from the user during registerationa and whenever customer logs in, password will be sent to the registered mobile number. In this case, during testing - imagine what will happen if the tester missed to find out that the users are able to register without giving mobile number. This defect of not asking for mobile number, will lead to other defects like (Log in failed due to NO mobile number, etc). This is known as Defect Cascading.
A defect is missed or not noticed during one phase (Here Mobile number is mssing). Due to this defect, you may get sequence of defects at later phases.
Defect cascading is an issues web based bug which is caused by another defect or issues. In this one defect invokes the other defect in the application. When a defect is present in any stage but is not identified, hide to other phases without getting noticed. This will result in increase in number of defects.
A defect is nothing but a deviation or variation from the expected result. When the original business requirements are not met, it leads to a defect. In other words, when the expected results do not match with the actual results, a bug arises.The cost of defects can be measured by the impact caused by the defects and when we discover them. Prior the defect is discovered, lesser is the cost of it.
Defect cascading is nothing but identification of a defect/bug which down the line have a potential of creating or becoming a cause for many other defects i.e these are the kind of defect which are not identified at a particular testing/development phase but they are hidden and reveal themselves in other phases.Further, these kind of defects cannot be fixed until and unless a proper root cause analysis is performed by the dev/testing team for its identification and fixage purpose.Rest, Below are some of the examples which were encountered by quality assurance services provider during different phases of testing:
Stage 1:Under Registration Page, 'Mobile Number' field is not kept mandatory(which is a bug and its unnoticed) and user while registering to the site DO NOT provide its mobile number and successfully registers.
Stage 2: Under Login Page, when user tries to login via 'Mobile Number'[As per the login page functionality a OTP(One Time Password) will be send to User’s registered mobile number] he/she will not be able to do so as while registering to the site mobile number was not provided.
In short, the root defect which was on 'Registration Page' lead to 'Login Page' too which resulted as another defect.
I hope my answer helped.