What does O(n) mean

Yuri Gurevich. What does O(n) mean. SIGACT News, 17(4):61-63, 1986. [doi]

@article{Gurevich86,
  title = {What does O(n) mean},
  author = {Yuri Gurevich},
  year = {1986},
  doi = {10.1145/8307.8311},
  url = {https://doi.org/10.1145/8307.8311},
  researchr = {https://researchr.org/publication/Gurevich86},
  cites = {0},
  citedby = {0},
  journal = {SIGACT News},
  volume = {17},
  number = {4},
  pages = {61-63},
}