The Indian Calendar is based on the sun and moon. As a result, you find that it has a solar year but lunar month. These 12 lunar months describe the whole year and help to identify the transition to the next orbit around the earth.
At the same time, the Hindu calendar tracks the solar months that in turn are described and named after the Zodiac signs that the Sun traverses during various parts of the year (as observed from the Earth). While lunar months are commonly used to define religious events and festivals, the solar months are used for civil purposes. These are then called as the civil months.