SAAS GLOSSARY · 56+ TERMS

Every SaaS term a founder actually needs.

MRR, ARR, CAC, LTV, churn, PMF, burn rate, runway — 56 essential SaaS metrics, startup terms, and product concepts with formulas, examples, and rules of thumb. Written for founders, not textbooks.

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Every term, alphabetised. Click any for the full definition, formula, and examples.

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How to use this glossary

This glossary is written for practitioners, not students. Every entry is a definition you can use inside a board deck, a pricing conversation, or a strategy doc today — not a textbook explanation you need a course to unpack. Most entries include three parts: the short definition, the formula or calculation (when one exists), and a rule of thumb that tells you what a “healthy” value looks like for a SaaS in the first 24 months.

The terms fall into four rough buckets, and which ones matter depends on what stage you are in. Pre-revenue founders should get fluent in PMF, ICP, TAM/SAM/SOM, MVP, and CAC payback before anything else — these shape what you build and who you build it for. Early-revenue founders (<$10k MRR) live inside MRR, ARR, churn, LTV, gross margin, and activation rate — the metrics that tell you whether growth is worth accelerating. Scaling founders (<$1M ARR) add net revenue retention, expansion MRR, CAC/LTV ratio, Rule of 40, and magic number — metrics that predict capital efficiency. Anyone running a team cares about burn multiple, runway, default alive/dead, and cash conversion score.

A few patterns to watch for. First, the same metric is often calculated three different ways across tools (e.g., churn can be customer churn, revenue churn, or net revenue churn — and they tell different stories). When this glossary gives a formula, that is the version we use; if your dashboard shows a different number, check which variant it is computing before you panic. Second, “good” ranges shift by motion: a PLG self-serve SaaS has very different healthy CAC, churn, and ACV than an enterprise sales-led product. When a rule of thumb is motion-dependent, we call it out. Third, vanity metrics (total signups, page views, GitHub stars) are deliberately excluded — they are not in the glossary because they rarely help founders decide anything.

If a term you use regularly is missing, email hello@planmysaas.com — we add requested terms within a week and credit the reporter.