IFRS 15 defines 'control' as the ability to direct the use of, and obtain substantially all of the remaining benefits from, an asset. This includes the ability to prevent other entities from directing the use of, and obtaining the benefits from, the asset.

The transfer of control of a good or service to a customer is a critical concept under IFRS 15 as it determines the point at which revenue is recognized. The standard provides the following indicators to help determine when control has been transferred:

1. The entity has a present right to payment for the asset. This indicates that the customer has control over the asset, as the entity has the right to receive payment for it.
2. The customer has legal title to the asset. Legal ownership often coincides with control over the asset.
3. The entity has transferred physical possession of the asset. Physical possession often indicates control, although it's not always conclusive. For example, a customer may not have control of a good that's been physically delivered if there are conditions that prevent the customer from the ability to direct the use of, and obtain the benefits from, the asset.
4. The customer has the significant risks and rewards of ownership of the asset. The transfer of risks and rewards often indicates a transfer of control, although it's not always conclusive.
5. The customer has accepted the asset. Customer acceptance might indicate that it has control over the asset. Acceptance could be formalized through a contract, or it might be implied by business practices or laws and regulations.

It's important to note that the determination of when control is transferred requires judgment and might vary depending on the nature of the goods or services provided and the terms and conditions of the contract.

Now let's take an illustrative example to understand how the concept of 'control' under IFRS 15 works.

Suppose that XYZ Manufacturing Co., a producer of large machinery, enters into a contract to sell a machine to ABC Corp. According to the contract terms, the machine is to be manufactured to ABC Corp's specifications, and the machine cannot be redirected to another customer or repurposed without significant costs. Payment is due from ABC Corp upon completion of the machine.

Here's how we can look at the indicators of the transfer of control:

1. The entity has a present right to payment for the asset: XYZ Manufacturing Co. has the right to payment once the machine is completed, indicating that ABC Corp has control once the manufacturing process is completed.
2. The customer has legal title to the asset: The legal title is transferred to ABC Corp when the machine is completed, signaling that control has passed.
3. The entity has transferred physical possession of the asset: Once the machine is completed, it's ready for physical delivery to ABC Corp. Though XYZ Manufacturing Co. might still physically possess the asset if ABC Corp has not yet collected it, control can be considered transferred as the company can't repurpose or sell the machine to another customer.
4. The customer has the significant risks and rewards of ownership of the asset: ABC Corp assumes the risks and rewards of ownership once the machine is completed.
5. The customer has accepted the asset: ABC Corp's acceptance of the machine may not be explicit but can be assumed once the machine is manufactured to ABC Corp's specifications and ready for delivery.

Therefore, XYZ Manufacturing Co. should recognize revenue from the sale of the machine when it is completed, as this is the point at which control of the machine is transferred to ABC Corp according to the indicators provided by IFRS 15.