Humoral immunity

The humoral immune system is a part of the immune system which defends the body against invading organisms and other foreign material.
The humeral part is done by macromolecules outside the cells. These may be secreted antibodies, complement proteins, or certain antimicrobial peptides. Their job is to attack bacteria (and other foreign substances) which are loose in the blood stream or other fluids. In older medicine, these fluids were called "humors". Both the more primitive innate immune system, and the later acquired or adaptive immune system of vertebrates, have humoral components.
The humoral immune system contrasts with the cell-mediated immunity. That involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.
How the humoral system works.
The main cells that make it work are the B cells, which create and secrete antibodies that seek out the invaders and attach to them. Once the invader is coated in antibodies, this targets the invader for destruction by other parts of the immune system. Before the B cell can create antibodies, it first needs T helper cells to 'teach' the B cell about details of the incoming invader. This is a key part of the adaptive immune system, and the reference attached here summarizes the process.
The production of antibodies tailor-made to combat particular bacteria is the most important element, but there are a number of other humeral defenses from the more primitive innate immune system.