Services
(1) If the Rajya Sabha declares by a two-thirds majority (of those present and voting) that it's necessary in the national interest, Parliament may create one or more All-India Services (including an all-India judicial service) common to the Union and states, regulating their recruitment and service conditions. (2) The IAS and IPS (as they existed at the Constitution's commencement) are deemed created under this article. (3)-(4) An all-India judicial service (if created) cannot include posts below district judge rank, and its creating law may amend Chapter VI of Part VI as needed, without being treated as a constitutional amendment.
This is the constitutional basis for India's distinctive "All-India Services" system - most famously the IAS (Indian Administrative Service) and IPS (Indian Police Service) - where officers are recruited by the Union but serve in postings across both Union and state governments, creating a genuinely pan-Indian civil service cadre that helps bind the country's administration together, rather than entirely separate Union and state bureaucracies.
This is why an IAS officer might spend part of their career serving in a state government administration and another part in a central government ministry - the same officer cadre serves both levels of government, which is exactly what this article's "common to the Union and the States" language creates.