Accruals are the non-cash net income earned by a business as a result of accrual based accounting. Mathematically, they are Net Income less Cash Flows from Operations.
Businesses with large positive accruals generally have large non-cash earnings like sales on account that have not yet been paid by customers. Those with negative accruals often are paid up-front for services and recognize the revenue over time as they perform the pre-paid service (newspapers are a good example of this type of business), or they may have large non-cash expenses such as depreciation.
Beware of businesses that have large positive accruals over long periods of time. They are a signal of low quality earnings numbers (earnings without much actual cash behind them, in a simple sense). Accruals are also a key element of the Beneish M-Score which detects earnings manipulation, and companies with higher accruals relative to their assets are more likely to have been manipulating earnings.
Accruals = (Net Income) - (Cash Flows from Operations)
YCharts calculates accruals using quarterly numbers.