"Layoffs" are the temporary or permanent release of employees from a company due to downsizing or restructuring or other business reason, as opposed to discipline or individual terminations.
Originally, "layoffs" were temporary, to reduce the labor expense during periods of low sales or lagging profits. Often the employees would be re-activated or rehired preferentially before any new employees. However, the term is now generally applied (as a euphemism for 'firings') to any mass reduction in the labor force of a company or industry, even permanent ones.