The Islamic legal term for making up a missed duty, such as a missed fast, is qada.
In Islamic jurisprudence, qada refers to performing a religious obligation after its appointed time has passed. For example, someone who misses Ramadan fasts because of illness, travel, menstruation, or another recognized reason may later complete those days as make-up fasts. The exact rules and deadlines can differ among legal schools and circumstances.
The Arabic term is associated with carrying out, fulfilling, or completing a matter. In legal usage, it can also relate to a judgment or adjudication, so its meaning depends on context. When discussing worship, however, qada generally means restoring an omitted or delayed obligatory act.
Qada is often confused with qiyas, which is analogical reasoning in law; ijma, scholarly consensus; and fatwa, a legal opinion. Qada is not itself a new type of fast: it describes the later performance of a duty that was missed.