If a company has receivables, this means it has made a sale but has yet to collect the money from the purchaser. Most companies operate by allowing some portion of their sales to be on credit. These type of sales are usually made to frequent or special customers who are invoiced periodically, and allows them to avoid the hassle of physically making payments as each transaction occurs. In other words, this is when a customer gives a company an IOU for goods or services already received or rendered.
Accounts receivable are not limited to businesses - individuals have them as well. People get receivables from their employers in the form of a monthly or bi-weekly paycheck. They are legally owed this money for services (work) already provided.
When a company owes debts to its suppliers or other parties, these are known as accounts payable.