According to food safety practices, cross-contamination occurs when:

Cross-contamination is a critical food safety issue that takes place when harmful microorganisms such as bacteria, viruses, or allergens are transferred from one food item or surface to another. This can happen in a variety of ways, such as using the same cutting board for raw meat and vegetables without proper cleaning in between, or when raw meat juices drip onto ready-to-eat foods. Understanding this concept is essential for preventing foodborne illnesses, as these microorganisms can lead to serious health risks if ingested.

The other options do not accurately describe cross-contamination. Storing food in a refrigerator, while important for maintaining proper temperatures for food safety, does not involve the transfer of germs. Cooking food at the wrong temperature can lead to undercooked food that may harbor harmful pathogens, but it doesn't involve cross-contamination. Leaving food out at room temperature is a risk factor for food spoilage and bacterial growth, but it doesn’t specifically describe the transfer of harmful germs between different food items or surfaces.