As sales leads are reviewed, they are measured against known requirements to pre-qualify them as a potential client of the product or service in question. For a sales lead to qualify as a sales prospect (or equivalently to move a lead from the process step sales lead to the process sales prospect) qualification must be performed and evaluated. Typically this involves identifying by direct interrogation the lead's product applicability, availability of funding, time frame for purchase. This is also the entry point of a sales tunnel or funnel.
Once a qualified lead exists, additional operations may be performed such as background research on the lead's employer, the generally market of the lead, contact information beyond that provided initially or other information useful for contacting and evaluating a lead for elevation to prospect, the next sales step.
If a sales lead eventually makes a purchase, this is called sales conversion. The ratio of sales leads that convert is often referred to as the conversion rate, a way to measure the effectiveness of a sales process, sales team, or sales person.