A prospect goes through different stages in the buying process related to the proximity to the decision making process. This distance can be measured by their interest, actions to purchase, for example:
Early Stage: this is when they are in the discovery of the solution to their problem or desire.
Intermediate stage: this is when you evaluate all the possibilities you have discovered and which of them best suits your specific needs.
Final stage: this is where you consider budget, payment methods, additional negotiations and are about to make the decision and payment.