Hi Vasu
As I understand it, it was a cowboy term for a wild horse. These days it is used to mean anyone who does not "follow the herd" i.e. who goes his/her own way and "bucks" the trends, making decisions very different from what most people are doing. A "fashion maverick" is the woman who wears a barely there mini-dress to an event where every other woman is in a ball gown. It often (but NOT always) refers to someone who is successful because they are different . The mini-dress woman with great legs is a maverick. The overweight 75 year old in the mini just needs help. The speaker may or may not approve of the maverick's choice.