Neointimal hyperplasia refers to proliferation and migration of vascular smooth muscle cells primarily in the tunica intima, resulting in the thickening of arterial walls and decreased arterial lumen space.[1][2] Neointimal hyperplasia is the major cause of restenosis after percutaneous coronary interventions such as stenting or angioplasty.[1] The term neointima is used because the cells in the hyperplastic regions of the vascular wall have histological characteristics of both intima and normal artery cells.[2]

Reference
Wiki: Neointimal hyperplasia