incidence
/ˈɪnsɪdəns; `ɪnsədəns/ n[sing]
1 ~ of sth extent to which sth happens or has an effect 事情发生或具有影响的程度; 发生率; 影响范围
This area has a high incidence of crime, disease, unemployment, etc. 这个地区的犯罪率、 发病率、 失业率等很高.
2 way in which a ray of light strikes a surface 光线向物体表面的照射; 入射
the angle of incidence 入射角.