The definition of a lead can vary from business to business and there is no set rule as to 'what's a lead?' A lead is generally a contact person that has come to your company from any number of channels regarding information on a product or service. A common way to capture leads like this is on a website. They can also be people that have attended a marketing event like a tradeshow, or someone you met at a seminar.
Details for a lead at that stage are normally high level and each business will have their own lead conversion policies, ie. "when to convert a lead or not to convert a lead". Generally, at some point in time a lead will either be closed (for example "a dead lead"), or it will be converted, once it is qualified. When a lead gets converted it becomes an opportunity.
One measure of marketing campaign success is the number of leads that the campaign generates.
Details for a lead at that stage are normally high level and each business will have their own lead conversion policies, ie. "when to convert a lead or not to convert a lead". Generally, at some point in time a lead will either be closed (for example "a dead lead"), or it will be converted, once it is qualified. When a lead gets converted it becomes an opportunity.
One measure of marketing campaign success is the number of leads that the campaign generates.