  We discuss k-strings in the large-N Yang-Mills theory and its supersymmetric
extension. Whereas the tension of the bona fide (stable) QCD string is expected
to depend only on the N-ality of the representation, tensions that depend on
specific representation R are often reported in the lattice literature. In
particular, adjoint strings are discussed and found in certain simulations. We
clarify this issue by systematically exploiting the notion of the quasi-stable
strings which becomes well-defined at large N. The quasi-stable strings with
representation-dependent tensions decay, but the decay rate (per unit length
per unit time) is suppressed as Lambda^2 F(N) where F(N) falls off as a
function of N. It can be determined on the case-by-case basis. The quasi-stable
strings eventually decay into stable strings whose tension indeed depends only
on the N-ality.
  We also briefly review large-N arguments showing why the Casimir formula for
the string tension cannot be correct, and present additional arguments in favor
of the sine formula. Finally, we comment on the relevance of our estimates to
Euclidean lattice measurements.
