Certain preparations contain killed or weakened live biological agents that, upon injection into our body, protect the body against those pathogens. What are these preparations called?

They are called vaccines

Vaccines which contain killed or weakened live biological agents upon injecting into the body and protect our body against those pathogens are called attenuated vaccines. The pathogens are either dead or are removed of their virulence, such that the antigens present on the surface of pathogens are able to cause production of relevant antibodies in the body. Production of antibodies also causes a memory to be stored in B cells of immune system such that if the same pathogen infects the organism next time, then memory can be stimulated and correct antibodies can be produced to combat the pathogen.