Meaning -A background task is a program that is running in the background even when the user is not necessarily interacting with it. When we use a computer, there are certain applications that need to keep updating over a period of time, in order to give you updated notifications or alerts. The only way to achieve this is for the task to keep running in the background, even after the user has closed the window on the desktop.
Applications like messengers, web browsers, conferencing apps, atc. all tend to keep working in the background even of they are not being used specifically by the user. One of the drawbacks of this is that more background tasks lead to the system slowing down as some of these applications hog on the RAM and make the other active applications sluggish.
The best way to avoid such scenario, is to turn off the applications entirely, even from the background.