Structural usage:

• A structural member that crosses any two other elements
• A primitive fastener consisting of a post barring a door
• The top tube of a bicycle frame
• The horizontal member of many sports goals including those for hockey, soccer, and American football
• A horizontal member of an electricity pylon, that carries the conductors

Networking and electronics usages:

• A crossbar switch
• Specifically, a 1XB or 5XB telephone switch, also known as Crossbar #1 or Crossbar #5
• A circuit composed of crossbar latches