An experience letter request asks a former or current employer to issue a work experience certificate confirming your role, dates and responsibilities. Send it to HR rather than your old manager, include your employee ID and exact employment dates so they can find your record quickly, and say what you need it for — visa, higher studies or a new employer — because that determines the wording they use.
An experience letter confirms what you did and for how long. A relieving letter confirms that you completed your notice period and were formally released. New employers in India and the Gulf frequently ask for both.
Practice varies by jurisdiction. Many employers issue one as a matter of policy, and some labour laws require a service certificate on request. If they refuse, offer letters, payslips and tax records are usually accepted as alternative proof.
HR or the people operations team, with your reporting manager copied. Managers rarely have the authority to issue letterhead documents themselves.