Seeds of some plants are unable to germinate even when conditions are favourable. This is called
Quiescence
Non-viability
Dormancy
Vivipary
Seed dormancy is the innate inhibition of germination of a viable seed placed in the most favourable environment for germination.
Rhizophora shows a special mode of seed germination called vivipary, in which seed germinates inside the fruit while still attached to the parent plant.