Serious delinquency is a situation in which payments on a mortgage are ninety days overdue. Serious delinquencies are more extreme versions of regular delinquencies. This can trigger a bank to begin the process of foreclosure. Banks consider serious delinquencies a strong indicator that the borrower may default on loan repayment.
Delinquency periods, or periods when a loan payment is overdue, are common. Most of the time, the borrower simply pays the payment a bit late, and proceedings continue as normal. However, once a delinquency period extends to a certain point, in this case, ninety days, it means that the bank usually isn't willing to wait anymore. The bank can either foreclose upon the person, or try to negotiate a forbearance, or other repayment option. Foreclosing can be complicated and time consuming for the bank, so alternative options are often desirable.