Final answer:
The organizational structure best classified for a company where employees move from project to project and employment depends on project availability is a Project organization.
Step-by-step explanation:
The organizational structure described in the question is Project organization. This is because employees move from one project to another, and there is a sense of temporariness linked to employment based on project availability. In project organizations, teams are formed for a specific project, and once the project ends, the team is disbanded, and members need to find new projects to sustain their employment. This structure contrasts with a functional organization, where employees have definite roles within a department, and with a matrix organization, where individuals may report to multiple managers for different projects but retain their employment independent of any single project's conclusion.