How is right of abode different from indefinite leave to remain?

Both let you live and work in the UK without a time limit, but they are legally different. Indefinite leave to remain is granted under the immigration rules and can be lost, for example if you spend a continuous period of two years or more outside the UK.

Right of abode sits outside immigration control altogether, so it cannot lapse through absence. For people who qualify, it is therefore a more secure status, though it is only available to British citizens and a narrow group of Commonwealth citizens, not to migrants generally.