Federation is a term used in the context of FIDE, the international governing body for chess. Every FIDE registered player must belong to a national governing body (federation). In the case of players born in and living in Ireland, their federation would normally be Ireland (or IRL, as it's common to use 3-letter country codes to denote federation - see full list) and they would typically be registered with the national body responsible for running chess in Ireland, the ICU, before being registered with FIDE.
Players do not register with FIDE themselves. Instead they normally become registered as a result of playing in a FIDE rated tournament for the first time. The information required to register a player (name, gender, date of birth and federation) will often come from data held by a national federation and typically be submitted to FIDE by a national rating officer.
Players living in Ireland but not born there would normally have a choice as to which federation to join (Ireland or any country for which they have a passport) and this choice is usually made at the time of joining the ICU (when players are required to state their federation). It can be changed at any time before the player is actually registered with FIDE.
Players already registered under another federation and wishing to change to IRL have to go through either a correction or a transfer process, depending on circumstances, and the latter involves a fee payable to FIDE.
Some care is needed in choosing your federation, if you have a choice.
- You cannot represent any federation in FIDE events other than the one you are registered with.
- Once registered, FIDE may charge a fee if you want to change federation.
- The governing body of the federation you register with will probably have (and do in the case of IRL) additional eligibility rules (such as length of residency) for representing their federation.