The 48 Hour Rule refers to the part of the mortgage allocation process related to the purchase and sale of Mortgage Backed Securities (MBS) to be announced (TBA).
A 5/6 Adjustable Rate Hybrid Mortgage (ARM 5/6 Hybrid) is a fixed rate mortgage for the first five years and then adjusted every six months thereafter.
The 500 shareholder threshold was a rule set by the SEC that required companies to publicly disclose financial statements and other information if they reached 500 or more individual shareholders.