SQL
SQL (sales qualified lead) is a term for a potential customer who, after being analyzed and verified by the marketing and sales departments, has been deemed ready to move to the next stage in the sales process.
The engagement phase has been surpassed by this person - such a customer is determined to purchase a product or service and has met the main qualification criteria by which the company determines whether the buyer is suitable.
Sales funnel and SQL

When considering a sales qualified lead, it is worth looking at the graphical presentation of the sales funnel prepared by Industrial Marketing Today and distinguishing marketing qualified leads from sales qualified leads.
Only after meeting certain criteria and gaining acceptance from the sales department can such a lead be passed to the sales team to complete the sales process.
Read also:
Useful links:
https://www.leadfuze.com/what-is-a-sales-qualified-lead-sql/
https://www.ringdna.com/blog/how-to-define-a-sales-qualified-lead