impaction

Short definition from Wiktionary

Noun

1. 1
   Compression; the packing together of loose matter.
2. 2
   something packed together tightly; a mass of densely-packed matter
3. 3
   A solid, immobile bulk of stool.
4. 4
   Failure of a tooth to erupt into the dental arch, because of adjacent teeth, dense overlying bone, excessive soft tissue, or other factor.
5. 5
   The situation where an educational institute, usually a college or university, receives more applications from qualified applicants than the number of spaces available, meaning that meeting the minimum admission requirements does not guarantee acceptance.