What term describes the action of applying minor changes to existing systems?

The term that best describes the action of applying minor changes to existing systems is "updates." Updates typically refer to small modifications or improvements that enhance the functionality, performance, or security of a system without overhauling it entirely. These changes can include bug fixes, security patches, or minor feature additions.

In contrast, upgrades usually refer to more significant changes that often involve replacing existing software or hardware with newer versions. Overhauls imply a comprehensive and extensive reworking of systems, which is far beyond minor tweaks. Installations involve the setup of new systems or software, not modifying existing ones. Thus, updates are specifically aimed at keeping systems current and functioning optimally through minor alterations.