A target market is the group of customers the business is set up to serve well.
Why naming it lowers cost
A message written for everybody persuades nobody, and it has to be advertised everywhere.
A message written for a specific group can be placed where that group is, and says something they recognise — which is why targeted marketing produces a lower cost per lead than broad marketing at the same spend.
What defines one for a service business
Geography, which is usually the strongest filter — see geographic expansion.
Property or business type: older homes, new build, commercial premises, a particular sector.
The job to be done: emergency repair, planned replacement, ongoing maintenance. These attract genuinely different customers with different price sensitivity.
Value: whether the business is built for high-volume small jobs or fewer larger ones — see increasing average job value.
The objection
That narrowing turns work away. In practice most small businesses cannot serve everyone anyway, and the choice is between choosing deliberately and having it chosen by whoever calls.
Nothing prevents taking work outside it. The target market decides where effort and money go, not what is accepted.
Market share
The proportion of the available market a business holds. For a local trade it is rarely knowable with precision and rarely worth pursuing precisely — the useful version is whether the business is winning more of the work it competes for, which is close rate.
Reviewing it
The target market and the actual customer base drift apart. Comparing who the business says it serves against who it actually invoices is a short exercise that frequently reveals the marketing is aimed at the wrong group — see market research.