1) Legal terminology 
An effective date or as of date is the date upon which something is considered to take effect. This may be different from the date upon which the event actually occurs or is recorded. ...
In an interest rate swap, the date the swap begins accruing interest.
In an interest rate swap, the date the swap begins accruing interest. 
The date on which a policy's coverage of a risk goes into effect. 
The date given in an EU Directive as the deadline for incorporation into national legislation.
The convexity of a bond calculated using cash flows that change with yields.
The date on which coverage under a health benefits plan begins.
The date a corporate action is effective and resultant new cash and/or stock are distributed.
The date at which a contract or statutory obligation commences. The effective date may be different than the date a contract is signed or a statute is enacted. For example, the effective date for the Copyright Act of 1976 is January 1, 1978.
Is the day that a new issue begins trading in the secondary market. This marks the transition from the initial issuance or Primary Market to the Aftermarket or Secondary Market. 
The date the policy becomes effective.