Using someone else's computers over the internet for specific tasks instead of doing everything on your own device. Like renting specialized equipment instead of buying it.
Google Drive is a cloud service that stores your files on Google's computers so you can access them from any device.
“Cloud service” is a general concept, not a single product. Each provider offers many cloud services (compute, storage, databases, AI, etc.) that you access over the internet and pay for based on usage.