NOUN (3)

1. a policy of creating strategic alliances in order to check the expansion of a hostile power or ideology or to force it to negotiate peacefully;
- Example: "containment of communist expansion was a central principle of United States' foreign policy from 1947 to the 1975";

2. (physics) a system designed to prevent the accidental release of radioactive material from a reactor;

3. the act of containing; keeping something from spreading;
- Example: "the containment of the AIDS epidemic"
- Example: "the containment of the rebellion"

The Collaborative International Dictionary of English v.0.48:

Containment \Con*tain"ment\, n.
   1. That which is contained; the extent; the substance. [Obs.]
      [1913 Webster]

            The containment of a rich man's estate. --Fuller.
      [1913 Webster]

   2. the act of containing.
      [PJC]

   3. (Diplomacy) the act or policy of restricting the influence
      or territorial growth of a hostile nation.

   Note: The policy of containment is employed when the defeat
         of a hostile nation or overthrow of its government is
         considered impractical or too costly.
         [PJC]

   4. the act of restricting some deleterious substance within a
      confined space, especially when such material is released
      unintentionally or by accident; as, containment of nuclear
      waste; containment of an oil spill. Also used
      attributively, as a containment boom.
      [PJC]

   5. a structure surrounding a nuclear power plant designed to
      prevent release of radioactive materials into the
      environment in the event of an accident.
      [PJC]

WordNet (r) 3.0 (2006):

containment
    n 1: a policy of creating strategic alliances in order to check
         the expansion of a hostile power or ideology or to force it
         to negotiate peacefully; "containment of communist
         expansion was a central principle of United States' foreign
         policy from 1947 to the 1975"
    2: (physics) a system designed to prevent the accidental release
       of radioactive material from a reactor
    3: the act of containing; keeping something from spreading; "the
       containment of the AIDS epidemic"; "the containment of the
       rebellion"