It means to fast one day for one day, which can be performed sporadically as well as on successive days. If another Ramadân intervenes while one is fasting intermittently, one fasts for the Ramadân first. A person who is so old that he will not be able to perform the fast of Ramadân or his fasts of qadâ till his death, and an invalid person whose recovery is beyond hope, must eat secretly. If he is rich, for each day he gives one fitra, that is, five hundred and twenty dirhams [seventeen hundred and fifty grams] of wheat or flour or its equivalent in gold or silver money to one or more poor people. The total amount may also be given to one poor person all at once at the beginning or end of Ramadân. If he recovers after giving the fidya he performs his fasts of Ramadân as well as his fasts of qadâ, (i.e. those which he did not perform on account of his illness.) If he dies without giving the fidya, he wills (before dying) for isqât. If he is poor, he does not give the fidya. He prays. If an old or invalid person of this kind cannot fast in hot or cold season, he makes qadâ in any season suitable for him. A person who cannot perform the salât standing as he fasts, fasts and performs the salât sitting. If a person breaks the fast or if a child becomes pubert or if a disbeliever becomes a Muslim or if a musâfir comes back to the city where his home is or – 67 –  Please see the twenty-first chapter for ‘isqât’. if a woman becomes pure (of menstruation); they must abstain (from eating, etc.) as if they were fasting till evening that day. The musâfir and the woman make qadâ of that day later.
Endless Bliss Page (67-68)