An accumulated dividend is a dividend that has not been paid in previous years but must be paid in the future, usually related to cumulative preference shares.

In the case of cumulative preference shares:

If dividend is not declared in a year,

It is carried forward (accumulated),

And must be paid before any dividend is given to equity shareholders.

Example:
If a company skips preference dividend for 2 years, those unpaid amounts become accumulated dividends and must be cleared later.

In simple terms, accumulated dividend is a past unpaid dividend that the company is obligated to pay in the future.