Final answer:
A localized infection occurs when pathogens enter the body and remain confined to a specific tissue or area, not spreading widely.
Step-by-step explanation:
The term that describes the extent of host involvement when microbes enter the body and remain confined to a specific tissue or area (at the portal) is localized infection. A localized infection occurs when the pathogen causes a disease confined to a small area of the body, usually near the portal of entry. For instance, a boil caused by Staphylococcus aureus would be considered a localized infection as the bacterium remains largely contained to that small location, unlike systemic infections that spread throughout the body.