Mythology refers to stories and ideas that say something about a culture and its values. Usually myths are stories about the supernatural from the past that are not true.
The Greeks, Romans. Celts and Nordics
It is generally accepted today that the Greco Roman religion is mythology and stories the Ancient Greeks and Romans believed about their gods, goddesses and heroes are just stories. Very few people believe them today though there are attempts to revive the Hellenistic religion. The stories associated with the Nordic religion, Odin, Thor and the others are widely considered mythical as well. Some people believe in the Nordic religion, it is called Asatru. The stories that go with the Celtic religion are also widely considered mythical though they can form part of New Age-ism.
Hindus have a wide range of stories about the gods, goddesses, heroes and heroines that they believe played a part in India’s magical past. Outsiders are unlikely to see any qualitative difference between these stories and other mythologies. Indeed many Hindu gods are related to Greeko-Roman gods. People who were indoctrinated into believing Hinduism during their impressionable childhood naturally tend to believe that Hindu religious stories are true while the stories of other religions are mythological.
Jews and Christians
The Bible contains any number of stories that resemble other religious traditions about supernatural events. This applies to the Old Testament and the New Testament. There is no reason to treat these stories any differently form the myths of other religions. People who have been taught Judaism or Christianity during their impressionable childhood frequently have difficulty seeing that their mythology is as reasonable or unreasonable as other mythologies.