The goal is to discourage a repeat of risky past practices, but the legislation makes an exception to the risk-retention standard for what is labeled a “qualified residential mortgage.” It is the still-unspecified definition of what’s become the industry’s latest acronym to digest, QRM, that has lenders in an uproar. If a very strict definition is applied by regulators, and a final rule isn’t expected until the spring, it could become more difficult, and more costly, for homebuyers to secure mortgage financing.