Naive T cells:

• Are T cells that are differentiated and have been released by the thymus but have not yet encountered their corresponding antigens
• Are considered immature and inactivated
• Undergo activation by antigen-presenting cells (APCs)
• Occur in the lymphoid tissue

Effector T cells:

• Are T cells that develop from naive T cells after having encountered their corresponding antigens
• Are considered mature and activated 
• Arise in non-lymphoid tissue
• Secrete cytokines that support activation of B and T cell, induce regulatory lymphocytes, and activate innate leukocytes