Final answer:
The terms 23-valent and 7-valent refer to pneumococcal vaccines and indicate the number of Streptococcus pneumoniae serotypes they target, with 23-valent covering 23 serotypes and 7-valent covering 7 serotypes.
Step-by-step explanation:
When terms like 23-valent and 7-valent are mentioned, they are typically referring to vaccines, specifically pneumococcal vaccines. These numbers indicate the number of serotypes of Streptococcus pneumoniae that the vaccine targets. The 23-valent pneumococcal polysaccharide vaccine (PPSV23) covers 23 different serotypes of pneumococcal bacteria, which are responsible for causing a range of diseases from pneumonia to meningitis. Meanwhile, the 7-valent pneumococcal conjugate vaccine (PCV7) covers 7 serotypes. The choice of vaccine depends on factors such as the age and health condition of the individual being vaccinated.