Someone who receives a 1099 is an independent contractor hired one project (or contract) at a time. They are not an employee of the company and their employment stops when the contract is complete. A 1099 worker may have multiple contracts with multiple businesses over a single year and their income varies accordingly. Most gig employees are 1099 workers.
Someone who receives a W-2 is an employee and is paid either hourly wages or a salary. A W-2 employee expects that their job and salary will continue until they leave or are let go from a position.