How different is it to have an application idea and a startup idea?
A good (and important) question!
An idea is mostly just a guess for a solution that solves a problem you guessed. Put that way, an idea is not a lot! There can be good ideas solving problems that don’t exist (or that are not important enough for people to pay attention or even money). But even if an idea is a solution to a validated problem, the idea is worth nothing until executed well (i.e. turned into a business with a product or service and an entire business model).
A startup is a company in search of a viable business model. A startup tries out business models and validates guesses about solution ideas, but also about about problems to solve, channels to deliver solutions through, ways to do this economically (i.e. make money) and so on. In that sense, ideas are the input to the startup motor: they represent the guesses that need to be validated, changed and validated again until a successful business model is found.
As a coach for startups I have people approaching me almost daily with “ideas”. Many know, that ideas are worth nothing until validated and executed well. The people who claim, that their idea would already be worth huge shares of a future company I turn down immediately — they have no understanding of how to build a successful business and use ideas. The most successful entrepreneurs, however, and the ones I like most to work with, are those who approach me with a target audience in mind and a problem to solve! These people are not preoccupied with their solution idea being the only way to fame and fortune and are humble enough to learn about the market. Businesses built by this rare lot of people tend to be the successful businesses, that turn startups (companies searching for a business model) into solid businesses (companies executing a validated business model actually making money and delivering value).
Btw a great tool to validate your ideas and turn them into successful business models is the Business Model Canvas. If you don’t know it, you should learn how to use it now!