A link which has a link diagram
with alternating underpasses and overpasses.

The proportion of links which are alternating tends exponentially to zero with increasing crossing number (Sundberg and Thistlethwaite 1998, Thistlethwaite 1998).

Hoste, J.; Thistlethwaite, M.; and Weeks, J. "The First ." Math. Intell.20,
33-48, Fall 1998.Menasco, W. and Thistlethwaite, M. "The Classification
of Alternating Links." Ann. Math.138, 113-171, 1993.Sundberg,
C. and Thistlethwaite, M. "The Rate of Growth of the Number of Prime Alternating
Links and Tangles." Pacific J. Math.182, 329-358, 1998.Thistlethwaite,
M. "On the Structure and Scarcity of Alternating Links and Tangles." J.
Knot Th. Ramifications7, 981-1004, 1998.