A CPV (Common Procurement Vocabulary) code is a standardised numeric code that classifies what a public tender is buying. Contracting authorities across the EU use the same codes, so searching by CPV finds relevant tenders regardless of language or wording.
CPV codes are eight digits plus a check digit and are hierarchical: the first two digits identify a broad division (for example 45 for construction or 72 for IT services), and further digits narrow the classification. Because they are language-independent and consistent across buyers, CPV codes are the most reliable way to search and set up alerts for tenders.
In practice you need a list rather than a single code. Most suppliers use three tiers: specific codes for what they unambiguously deliver, adjacent codes for work they could credibly take on, and one or two two-digit divisions as a wide safety net for tenders a buyer classified unexpectedly. Coverage is high — the large majority of active tenders carry a code — but classification is done by the buyer and is not always accurate, which is exactly why the division-level tier is worth the extra noise it produces.