I don't know exactly how it works in the US (probably it varies by state), but to give an idea, in Canada employment can end typically in one of three ways: quitting, being fired, or being laid off. (Some other less common cases exist of course like long term injuries or medical issues etc.)

Generally being fired means it was somehow the employee's fault (anything from not being good enough at the job to being caught doing something actively wrong), while being laid off is due to lack of available work (when a business has to scale down, or dies completely). Laid-off workers can start collecting employment insurance almost immediately, and have certain rights to getting their job back if the company suddenly has work available again, among other things (i.e. it's not meant to be possible for employers to use layoffs as a way of getting rid of employees they can't or don't want to fire).

A fired employee can't get employment insurance as immediately since they're seen as at fault for their own job loss from a legal perspective, but if the firing was wrongful, then they might have legal recourse against their employer.

The US is again probably very different in details but the basic difference of employee-at-fault job loss vs the work no longer existing is essentially the same, I think.