infiltration

英[,ɪnfɪl'treɪʃən] 美[,ɪnfɪl'treʃən]

1. a process in which individuals (or small groups) penetrate an area (especially the military penetration of enemy positions without detection)

2. the slow passage of a liquid through a filtering medium;: "the percolation of rainwater through the soil"; "the infiltration of seawater through the lava"