Beam-struts

Beam refers to a structural element that primarily resists loads applied laterally to the beam's axis. They are the Horizontal members of the structure. It's mode of deflection is primarily by bending.
Struts are short members in an assembly of members that get compressed, as opposed to ties which are stretched. They are the Horizontal or Inclined member of the structure. It's mode of deflection is primarily by Tension.