Ontario's Employment Standards Act sets two separate statutory MINIMUM entitlements for employees terminated without cause. Termination pay (notice, or pay in lieu of working notice) scales from 1 week after just 3 months of service up to a maximum of 8 weeks at 8+ years, and applies to nearly every non-unionized employee let go without cause. It's calculated on your regular wages for a regular work week, this calculator uses annual salary ÷ 52 as that figure.
Severance pay is a genuinely separate, and often much larger, entitlement layered on top. It only applies if you have 5 or more years of continuous service AND your employer's Ontario payroll is $2.5 million or more, or the employer permanently discontinued the business and let go 50+ employees within a 6-month window. Where it applies, it's calculated as 1 week's pay per year of service (including partial years), capped at 26 weeks, regardless of how many decades you've worked there.
Both entitlements are statutory FLOORS, not the full picture. Most non-unionized Ontario employees are ALSO entitled to common law "reasonable notice", which courts assess individually using factors like age, seniority, and how readily comparable work is available, and which frequently exceeds the ESA minimum by a wide margin for longer-tenured, older, or senior employees. Whether your specific employment contract validly limits you to the ESA minimum, or whether you're entitled to the larger common law figure instead, is a legal question only an employment lawyer can properly answer for your situation.