Total addressable market
Total addressable market is the number of businesses that could plausibly buy what you sell. For outbound, the only version that matters is the one you can build a contact list for.
The figure quoted in pitch decks is a revenue number derived from an industry report, and it is useless for planning outreach. The operational version is a count: how many businesses match your profile, in the places you can sell to, right now.
You can measure it rather than estimate it. Run the profile as a search across your target locations and count the results. If physiotherapy clinics across twelve cities returns 2,800 businesses, that is the market, and every campaign assumption has to fit inside it.
This number decides whether outbound is even the right channel. A market of 300 businesses cannot absorb a volume strategy — it needs a small number of carefully written messages. A market of 40,000 can absorb a weekly cadence for years.