Azure websites Webjobs are currently in preview and they are nice way to have some light weight background processing for your websites. You might have faced scenarios where you would have spin up threads to perform some background tasks in your website. That's not an ideal way so you used to have another option of having PaaS worker roles, but do we really need them for small tasks such as some aggregation of data, reporting or log clean-up.

This is where Azure Webjobs come to rescue. They provide background processing for your websites. In other words we can call them - "light weight web worker role". 

There are different ways of scheduling jobs in Azure webjobs - we can schedule the jobs on daily, weekly basis or have them constant running. Constantly running job, for example, will look at an activity running in the website and react to it. It is kind of a trigger in websites. This is, basically, a continuously running task or service.

Different kinds of running modes that Webjobs provide:

It is basically a light weight web worker role, and we shouldn't do heavy tasks as it will run on top of the website itself. Also, there's no point in having a worker role just to run a 10 second jobs such as aggregation of data. In this case webjobs are helpful. Webjobs is managed, so everything is much easier to do. If you wanted to spin up a small application, you can do it within 1 minute using webjobs.

Websites are basically a container for webjobs. Webjobs run outside of your website and run parallel to w3wp process. Each job is a separate process running in the VM.