Accrued income is more often called accrued revenue, and that entry covers the topic in full: the journal entries, worked examples and how the amount is reversed once cash arrives. This page gives a short definition and explains the two names.
Accrued income is income a business has earned in a period but has not yet been paid for or, in many cases, has not yet invoiced. Under accrual accounting it is still recorded in the period it was earned, which follows the rules of revenue recognition. Common examples are interest earned on a deposit but paid next month, which appears as interest receivable, and work finished before the month-end bill goes out.
Both terms describe the same balance-sheet asset. "Accrued income" is the usual wording in the UK and in personal or investment contexts, while "accrued revenue" is the more common term in US company accounts. Once the customer is billed, the amount usually moves into accounts receivable. Its mirror image, cash received before it is earned, is deferred revenue.