All the current answers are using language that is perhaps correct as a definition, but not what would actually work in your situation.
The word you want to use in your phrases is "opportunity." A job opportunity is when there is the opportunity for a job. Nearly no company would describe this as a job offer until an actual job offer has been made.
It is also a very general term that can be used regardless of which stage you are in the process. This has the added benefit of not being presumptuous of your application state. You could for example turn down another interview request or a formal offer or an informal offer all with the same word.
An interview request is NOT an offer in nearly all cases.
- Thank you, but I am not interested in this opportunity.
- I am considering two other opportunities at the moment.
However, once they commit to making an offer it would be considered a "verbal offer." This is the state where the company has indicated they intend to give you a formal job offer, but not the actual paperwork yet. It might include as you describe the expected salary but doesn't include all the specific information.
In this case, I would still use the word opportunity in both the above contexts. The reason is that while well intentioned a verbal offer does not guarantee a formal offer. On The Workplace we get questions about this all the time. But it is still an opportunity.
A company is interested in a person as a potential employee, and contacts that person. The company's representative describes the role, advertises the benefits, interviews the person etc.
When the job is available to apply for, you would consider it a job posting / position. Once you have applied, but without having reciprocated interest, it'd become a job application. It can be considered to become an opportunity once you have communication back/forth from the company.
Best Answer
David is often used in reference to David and Goliath.
Story here.
Edit based on comments: They are right. It is all about context. In many contexts you would have to explain that the person is a David trying to bring down a Goliath. I have though seen the term David used alone when there is a build-up. If you were talking about someone trying to take out giants and said, "He will act like David with his slingshot..." There are tons of ways to do this. Was not implying that just simply mentioning the name David is proper, although some people would still get the inference.